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How does a car with keyless entry know where the key is?
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If I hold the car key and touch the handle on the door, the car locks the doors. But if I leave the key inside the car, it won't lock itself.
How does the car know where the key is located? What mechanism does it use to triangulate the key? It can't be using ultrasound since ultrasound doesn't go through objects and is directional. It can't be radio wave either, unless the car can accurately measure down to nanoseconds.
signal-processing automotive
asked 4 hours ago
Yu Zhou
1062
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Yu Zhou is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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add a comment |Â
up vote
1
down vote
favorite
If I hold the car key and touch the handle on the door, the car locks the doors. But if I leave the key inside the car, it won't lock itself.
How does the car know where the key is located? What mechanism does it use to triangulate the key? It can't be using ultrasound since ultrasound doesn't go through objects and is directional. It can't be radio wave either, unless the car can accurately measure down to nanoseconds.
signal-processing automotive
asked 4 hours ago
Yu Zhou
1062
New contributor
Yu Zhou is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
It is definitely RF. Don't forget a low frequency signal can be modulated on RF, so you assumption about nanoseconds does not hold.
– Eugene Sh.
4 hours ago
I have that for my car too, and I have been wondering the same. First thing I noticed is that it isn't that accurate. Sometimes, when I'm close to the door, it thinks the key is inside (which is annoying BTW). Then, what I know is that there are multiple antennas distributed at different locations in the vehicle (I don't quite remember if it's two or three). But then, I don't know the definitive answer. Maybe it is just a measure of the signal strength.
– dim
3 hours ago
I am more interested how the "walk-away" feature is working. This one is making me thing that the key has to repeatedly transmit, which is not going well with the battery lifetime.
– Eugene Sh.
3 hours ago
@Eugene Sh. The fobs presumably transmit only when a button is pressed or in response to a ping from the car, so the fob will only transmit when within range of the car, and then only when polled. Presumably the system could poll more frequently at some times than others to optimize response time vs battery life.
– ajb
2 hours ago
add a comment |Â
up vote
1
down vote
favorite
up vote
1
down vote
favorite
If I hold the car key and touch the handle on the door, the car locks the doors. But if I leave the key inside the car, it won't lock itself.
How does the car know where the key is located? What mechanism does it use to triangulate the key? It can't be using ultrasound since ultrasound doesn't go through objects and is directional. It can't be radio wave either, unless the car can accurately measure down to nanoseconds.
signal-processing automotive
asked 4 hours ago
Yu Zhou
1062
New contributor
Yu Zhou is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
If I hold the car key and touch the handle on the door, the car locks the doors. But if I leave the key inside the car, it won't lock itself.
How does the car know where the key is located? What mechanism does it use to triangulate the key? It can't be using ultrasound since ultrasound doesn't go through objects and is directional. It can't be radio wave either, unless the car can accurately measure down to nanoseconds.
signal-processing automotive
signal-processing automotive
asked 4 hours ago
Yu Zhou
1062
New contributor
Yu Zhou is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 4 hours ago
Yu Zhou
1062
New contributor
Yu Zhou is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 4 hours ago
Yu Zhou
1062
New contributor
Yu Zhou is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 4 hours ago
Yu Zhou
1062
asked 4 hours ago
Yu Zhou
1062
1062
New contributor
Yu Zhou is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Yu Zhou is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Yu Zhou is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
It is definitely RF. Don't forget a low frequency signal can be modulated on RF, so you assumption about nanoseconds does not hold.
– Eugene Sh.
4 hours ago
I have that for my car too, and I have been wondering the same. First thing I noticed is that it isn't that accurate. Sometimes, when I'm close to the door, it thinks the key is inside (which is annoying BTW). Then, what I know is that there are multiple antennas distributed at different locations in the vehicle (I don't quite remember if it's two or three). But then, I don't know the definitive answer. Maybe it is just a measure of the signal strength.
– dim
3 hours ago
I am more interested how the "walk-away" feature is working. This one is making me thing that the key has to repeatedly transmit, which is not going well with the battery lifetime.
– Eugene Sh.
3 hours ago
@Eugene Sh. The fobs presumably transmit only when a button is pressed or in response to a ping from the car, so the fob will only transmit when within range of the car, and then only when polled. Presumably the system could poll more frequently at some times than others to optimize response time vs battery life.
– ajb
2 hours ago
add a comment |Â
1
It is definitely RF. Don't forget a low frequency signal can be modulated on RF, so you assumption about nanoseconds does not hold.
– Eugene Sh.
4 hours ago
I have that for my car too, and I have been wondering the same. First thing I noticed is that it isn't that accurate. Sometimes, when I'm close to the door, it thinks the key is inside (which is annoying BTW). Then, what I know is that there are multiple antennas distributed at different locations in the vehicle (I don't quite remember if it's two or three). But then, I don't know the definitive answer. Maybe it is just a measure of the signal strength.
– dim
3 hours ago
I am more interested how the "walk-away" feature is working. This one is making me thing that the key has to repeatedly transmit, which is not going well with the battery lifetime.
– Eugene Sh.
3 hours ago
@Eugene Sh. The fobs presumably transmit only when a button is pressed or in response to a ping from the car, so the fob will only transmit when within range of the car, and then only when polled. Presumably the system could poll more frequently at some times than others to optimize response time vs battery life.
– ajb
2 hours ago
1
1
It is definitely RF. Don't forget a low frequency signal can be modulated on RF, so you assumption about nanoseconds does not hold.
– Eugene Sh.
4 hours ago
It is definitely RF. Don't forget a low frequency signal can be modulated on RF, so you assumption about nanoseconds does not hold.
– Eugene Sh.
4 hours ago
I have that for my car too, and I have been wondering the same. First thing I noticed is that it isn't that accurate. Sometimes, when I'm close to the door, it thinks the key is inside (which is annoying BTW). Then, what I know is that there are multiple antennas distributed at different locations in the vehicle (I don't quite remember if it's two or three). But then, I don't know the definitive answer. Maybe it is just a measure of the signal strength.
– dim
3 hours ago
I have that for my car too, and I have been wondering the same. First thing I noticed is that it isn't that accurate. Sometimes, when I'm close to the door, it thinks the key is inside (which is annoying BTW). Then, what I know is that there are multiple antennas distributed at different locations in the vehicle (I don't quite remember if it's two or three). But then, I don't know the definitive answer. Maybe it is just a measure of the signal strength.
– dim
3 hours ago
I am more interested how the "walk-away" feature is working. This one is making me thing that the key has to repeatedly transmit, which is not going well with the battery lifetime.
– Eugene Sh.
3 hours ago
I am more interested how the "walk-away" feature is working. This one is making me thing that the key has to repeatedly transmit, which is not going well with the battery lifetime.
– Eugene Sh.
3 hours ago
@Eugene Sh. The fobs presumably transmit only when a button is pressed or in response to a ping from the car, so the fob will only transmit when within range of the car, and then only when polled. Presumably the system could poll more frequently at some times than others to optimize response time vs battery life.
– ajb
2 hours ago
@Eugene Sh. The fobs presumably transmit only when a button is pressed or in response to a ping from the car, so the fob will only transmit when within range of the car, and then only when polled. Presumably the system could poll more frequently at some times than others to optimize response time vs battery life.
– ajb
2 hours ago
add a comment |Â
2 Answers
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active
oldest
votes
up vote
5
down vote
They either use multiple antennas for each exterior zone of the car and/or use RF in combination with other sensors, for instance detecting that the user has touched the front driver's side door handle.
An Atmel brochure about these "passive entry/passive start" systems describes the latter:
Passive Entry (PE)
The passive entry function allows the driver to unlock the
vehicle's doors without activating the key fob. However,
some user action is needed to trigger the system such as
approaching the door, or touching or pulling on the door
handle. When the vehicle detects such an activity, it starts to
search for the key fob outside the vehicle cabin. This is called
localization. Once the fob has been authenticated, the doors
unlock automatically
It includes this diagram of a typical system: 
The former system, consisting of multiple exterior antennas is described here by a manufacturer of magnetic components:
PKE Systems work by having a series of LF (low frequency, 20kHz, 125kHz & 134kHz) transmitter antennas, depending on chip-set used, both inside and outside the vehicle. External antennas are located in the door hadler, mirrors or trunk position. When vehicle is triggered either, close to vehicle, pulling the hadle or touching it an LF signal is transmitted from the antennas to the Key. Key is activated and transmited its ID back to the vehicle using RF channel, if Key code is correct the electronic module unlock the vehicle.
They include the following diagram:
In order to prevent the key from being locked in the car, both systems also include a set of antennas inside the car that are designed specifically to detect keyfobs that are specifically inside of the car. These, as well as the exterior localized antennas use lower RF frequencies presumably to improve localization of the signal. The ability of the interior antennas to discriminate keyfobs inside versus outside of the car is further helped by the car's shell being a large metal box that will help to impede the antennas from picking up keyfobs outside of the vehicle.
answered 3 hours ago
ajb
1,04249
add a comment |Â
up vote
1
down vote
Why would the car need to "know" where the key is?
Would knowing that the key is "nearby" be enough? I think it would.
Then triangulation is not needed. The key simply transmits a signal every few seconds or so. Or better: only when the key detects movement, it sends the signal. When the key is on a desk it can stop transmitting until you pick it up. That saves battery life.
Ultrasound just like normal sound does go through objects. Or can't you hear any sound from outside your car when you're inside your car. But ultrasound isn't used for car keys, it takes too much power, is too directional and there are better solutions.
For radio waves explain why a measurement down to nanoseconds is needed. Marconi managed to us radio signals without measuring down to nanoseconds.
A radio signal is used and that can be done in an extremely simple way. The RF signal at a certain frequency (defined by a cheap resonator or a crystal and a PLL circuit) is switched on/off in a certain sequence which represents the data being sent, see OOK Modulation
In the car a receiver picks up the signal, then demodulates it to retrieve the data sequence which is processed in a microcontroller. Garage doors and wireless remote controlled mains sockets often use the same system.
By limiting the transmitted power and/or required signal noise ratio the range at which this works can be limited so you can only unlock the car when it is nearby.
To make things more secure the data being send should not be the same each time, there are solutions for this like time changing codes etc.
In a more secure system the key could also house a receiver so two communication over RF with the car can take place.
But anyway: despite what you thought RF signals is what is used.
answered 3 hours ago
Bimpelrekkie
42.1k23790
3
The OP described the situation of a car needing to know "where" the key is, and not just if it is "nearby." Not locking the car door when the keys are inside vs outside?
– user2913869
3 hours ago
1
See the other answer, if you have enough antennas you can translate "nearby" into "where". OP was asking more questions that just the inside vs outside question.
– Bimpelrekkie
3 hours ago
add a comment |Â
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
5
down vote
They either use multiple antennas for each exterior zone of the car and/or use RF in combination with other sensors, for instance detecting that the user has touched the front driver's side door handle.
An Atmel brochure about these "passive entry/passive start" systems describes the latter:
Passive Entry (PE)
The passive entry function allows the driver to unlock the
vehicle's doors without activating the key fob. However,
some user action is needed to trigger the system such as
approaching the door, or touching or pulling on the door
handle. When the vehicle detects such an activity, it starts to
search for the key fob outside the vehicle cabin. This is called
localization. Once the fob has been authenticated, the doors
unlock automatically
It includes this diagram of a typical system:
The former system, consisting of multiple exterior antennas is described here by a manufacturer of magnetic components:
PKE Systems work by having a series of LF (low frequency, 20kHz, 125kHz & 134kHz) transmitter antennas, depending on chip-set used, both inside and outside the vehicle. External antennas are located in the door hadler, mirrors or trunk position. When vehicle is triggered either, close to vehicle, pulling the hadle or touching it an LF signal is transmitted from the antennas to the Key. Key is activated and transmited its ID back to the vehicle using RF channel, if Key code is correct the electronic module unlock the vehicle.
They include the following diagram:
In order to prevent the key from being locked in the car, both systems also include a set of antennas inside the car that are designed specifically to detect keyfobs that are specifically inside of the car. These, as well as the exterior localized antennas use lower RF frequencies presumably to improve localization of the signal. The ability of the interior antennas to discriminate keyfobs inside versus outside of the car is further helped by the car's shell being a large metal box that will help to impede the antennas from picking up keyfobs outside of the vehicle.
answered 3 hours ago
ajb
1,04249
add a comment |Â
up vote
5
down vote
They either use multiple antennas for each exterior zone of the car and/or use RF in combination with other sensors, for instance detecting that the user has touched the front driver's side door handle.
An Atmel brochure about these "passive entry/passive start" systems describes the latter:
Passive Entry (PE)
The passive entry function allows the driver to unlock the
vehicle's doors without activating the key fob. However,
some user action is needed to trigger the system such as
approaching the door, or touching or pulling on the door
handle. When the vehicle detects such an activity, it starts to
search for the key fob outside the vehicle cabin. This is called
localization. Once the fob has been authenticated, the doors
unlock automatically
It includes this diagram of a typical system:
The former system, consisting of multiple exterior antennas is described here by a manufacturer of magnetic components:
PKE Systems work by having a series of LF (low frequency, 20kHz, 125kHz & 134kHz) transmitter antennas, depending on chip-set used, both inside and outside the vehicle. External antennas are located in the door hadler, mirrors or trunk position. When vehicle is triggered either, close to vehicle, pulling the hadle or touching it an LF signal is transmitted from the antennas to the Key. Key is activated and transmited its ID back to the vehicle using RF channel, if Key code is correct the electronic module unlock the vehicle.
They include the following diagram:
In order to prevent the key from being locked in the car, both systems also include a set of antennas inside the car that are designed specifically to detect keyfobs that are specifically inside of the car. These, as well as the exterior localized antennas use lower RF frequencies presumably to improve localization of the signal. The ability of the interior antennas to discriminate keyfobs inside versus outside of the car is further helped by the car's shell being a large metal box that will help to impede the antennas from picking up keyfobs outside of the vehicle.
answered 3 hours ago
ajb
1,04249
add a comment |Â
up vote
5
down vote
up vote
5
down vote
They either use multiple antennas for each exterior zone of the car and/or use RF in combination with other sensors, for instance detecting that the user has touched the front driver's side door handle.
An Atmel brochure about these "passive entry/passive start" systems describes the latter:
Passive Entry (PE)
The passive entry function allows the driver to unlock the
vehicle's doors without activating the key fob. However,
some user action is needed to trigger the system such as
approaching the door, or touching or pulling on the door
handle. When the vehicle detects such an activity, it starts to
search for the key fob outside the vehicle cabin. This is called
localization. Once the fob has been authenticated, the doors
unlock automatically
It includes this diagram of a typical system:
The former system, consisting of multiple exterior antennas is described here by a manufacturer of magnetic components:
PKE Systems work by having a series of LF (low frequency, 20kHz, 125kHz & 134kHz) transmitter antennas, depending on chip-set used, both inside and outside the vehicle. External antennas are located in the door hadler, mirrors or trunk position. When vehicle is triggered either, close to vehicle, pulling the hadle or touching it an LF signal is transmitted from the antennas to the Key. Key is activated and transmited its ID back to the vehicle using RF channel, if Key code is correct the electronic module unlock the vehicle.
They include the following diagram:
In order to prevent the key from being locked in the car, both systems also include a set of antennas inside the car that are designed specifically to detect keyfobs that are specifically inside of the car. These, as well as the exterior localized antennas use lower RF frequencies presumably to improve localization of the signal. The ability of the interior antennas to discriminate keyfobs inside versus outside of the car is further helped by the car's shell being a large metal box that will help to impede the antennas from picking up keyfobs outside of the vehicle.
answered 3 hours ago
ajb
1,04249
They either use multiple antennas for each exterior zone of the car and/or use RF in combination with other sensors, for instance detecting that the user has touched the front driver's side door handle.
An Atmel brochure about these "passive entry/passive start" systems describes the latter:
Passive Entry (PE)
The passive entry function allows the driver to unlock the
vehicle's doors without activating the key fob. However,
some user action is needed to trigger the system such as
approaching the door, or touching or pulling on the door
handle. When the vehicle detects such an activity, it starts to
search for the key fob outside the vehicle cabin. This is called
localization. Once the fob has been authenticated, the doors
unlock automatically
It includes this diagram of a typical system:
The former system, consisting of multiple exterior antennas is described here by a manufacturer of magnetic components:
PKE Systems work by having a series of LF (low frequency, 20kHz, 125kHz & 134kHz) transmitter antennas, depending on chip-set used, both inside and outside the vehicle. External antennas are located in the door hadler, mirrors or trunk position. When vehicle is triggered either, close to vehicle, pulling the hadle or touching it an LF signal is transmitted from the antennas to the Key. Key is activated and transmited its ID back to the vehicle using RF channel, if Key code is correct the electronic module unlock the vehicle.
They include the following diagram:
In order to prevent the key from being locked in the car, both systems also include a set of antennas inside the car that are designed specifically to detect keyfobs that are specifically inside of the car. These, as well as the exterior localized antennas use lower RF frequencies presumably to improve localization of the signal. The ability of the interior antennas to discriminate keyfobs inside versus outside of the car is further helped by the car's shell being a large metal box that will help to impede the antennas from picking up keyfobs outside of the vehicle.
answered 3 hours ago
ajb
1,04249
answered 3 hours ago
ajb
1,04249
answered 3 hours ago
ajb
1,04249
answered 3 hours ago
ajb
1,04249
1,04249
add a comment |Â
add a comment |Â
up vote
1
down vote
Why would the car need to "know" where the key is?
Would knowing that the key is "nearby" be enough? I think it would.
Then triangulation is not needed. The key simply transmits a signal every few seconds or so. Or better: only when the key detects movement, it sends the signal. When the key is on a desk it can stop transmitting until you pick it up. That saves battery life.
Ultrasound just like normal sound does go through objects. Or can't you hear any sound from outside your car when you're inside your car. But ultrasound isn't used for car keys, it takes too much power, is too directional and there are better solutions.
For radio waves explain why a measurement down to nanoseconds is needed. Marconi managed to us radio signals without measuring down to nanoseconds.
A radio signal is used and that can be done in an extremely simple way. The RF signal at a certain frequency (defined by a cheap resonator or a crystal and a PLL circuit) is switched on/off in a certain sequence which represents the data being sent, see OOK Modulation
In the car a receiver picks up the signal, then demodulates it to retrieve the data sequence which is processed in a microcontroller. Garage doors and wireless remote controlled mains sockets often use the same system.
By limiting the transmitted power and/or required signal noise ratio the range at which this works can be limited so you can only unlock the car when it is nearby.
To make things more secure the data being send should not be the same each time, there are solutions for this like time changing codes etc.
In a more secure system the key could also house a receiver so two communication over RF with the car can take place.
But anyway: despite what you thought RF signals is what is used.
answered 3 hours ago
Bimpelrekkie
42.1k23790
3
The OP described the situation of a car needing to know "where" the key is, and not just if it is "nearby." Not locking the car door when the keys are inside vs outside?
– user2913869
3 hours ago
1
See the other answer, if you have enough antennas you can translate "nearby" into "where". OP was asking more questions that just the inside vs outside question.
– Bimpelrekkie
3 hours ago
add a comment |Â
up vote
1
down vote
Why would the car need to "know" where the key is?
Would knowing that the key is "nearby" be enough? I think it would.
Then triangulation is not needed. The key simply transmits a signal every few seconds or so. Or better: only when the key detects movement, it sends the signal. When the key is on a desk it can stop transmitting until you pick it up. That saves battery life.
Ultrasound just like normal sound does go through objects. Or can't you hear any sound from outside your car when you're inside your car. But ultrasound isn't used for car keys, it takes too much power, is too directional and there are better solutions.
For radio waves explain why a measurement down to nanoseconds is needed. Marconi managed to us radio signals without measuring down to nanoseconds.
A radio signal is used and that can be done in an extremely simple way. The RF signal at a certain frequency (defined by a cheap resonator or a crystal and a PLL circuit) is switched on/off in a certain sequence which represents the data being sent, see OOK Modulation
In the car a receiver picks up the signal, then demodulates it to retrieve the data sequence which is processed in a microcontroller. Garage doors and wireless remote controlled mains sockets often use the same system.
By limiting the transmitted power and/or required signal noise ratio the range at which this works can be limited so you can only unlock the car when it is nearby.
To make things more secure the data being send should not be the same each time, there are solutions for this like time changing codes etc.
In a more secure system the key could also house a receiver so two communication over RF with the car can take place.
But anyway: despite what you thought RF signals is what is used.
answered 3 hours ago
Bimpelrekkie
42.1k23790
3
The OP described the situation of a car needing to know "where" the key is, and not just if it is "nearby." Not locking the car door when the keys are inside vs outside?
– user2913869
3 hours ago
1
See the other answer, if you have enough antennas you can translate "nearby" into "where". OP was asking more questions that just the inside vs outside question.
– Bimpelrekkie
3 hours ago
add a comment |Â
up vote
1
down vote
up vote
1
down vote
Why would the car need to "know" where the key is?
Would knowing that the key is "nearby" be enough? I think it would.
Then triangulation is not needed. The key simply transmits a signal every few seconds or so. Or better: only when the key detects movement, it sends the signal. When the key is on a desk it can stop transmitting until you pick it up. That saves battery life.
Ultrasound just like normal sound does go through objects. Or can't you hear any sound from outside your car when you're inside your car. But ultrasound isn't used for car keys, it takes too much power, is too directional and there are better solutions.
For radio waves explain why a measurement down to nanoseconds is needed. Marconi managed to us radio signals without measuring down to nanoseconds.
A radio signal is used and that can be done in an extremely simple way. The RF signal at a certain frequency (defined by a cheap resonator or a crystal and a PLL circuit) is switched on/off in a certain sequence which represents the data being sent, see OOK Modulation
In the car a receiver picks up the signal, then demodulates it to retrieve the data sequence which is processed in a microcontroller. Garage doors and wireless remote controlled mains sockets often use the same system.
By limiting the transmitted power and/or required signal noise ratio the range at which this works can be limited so you can only unlock the car when it is nearby.
To make things more secure the data being send should not be the same each time, there are solutions for this like time changing codes etc.
In a more secure system the key could also house a receiver so two communication over RF with the car can take place.
But anyway: despite what you thought RF signals is what is used.
answered 3 hours ago
Bimpelrekkie
42.1k23790
Why would the car need to "know" where the key is?
Would knowing that the key is "nearby" be enough? I think it would.
Then triangulation is not needed. The key simply transmits a signal every few seconds or so. Or better: only when the key detects movement, it sends the signal. When the key is on a desk it can stop transmitting until you pick it up. That saves battery life.
Ultrasound just like normal sound does go through objects. Or can't you hear any sound from outside your car when you're inside your car. But ultrasound isn't used for car keys, it takes too much power, is too directional and there are better solutions.
For radio waves explain why a measurement down to nanoseconds is needed. Marconi managed to us radio signals without measuring down to nanoseconds.
A radio signal is used and that can be done in an extremely simple way. The RF signal at a certain frequency (defined by a cheap resonator or a crystal and a PLL circuit) is switched on/off in a certain sequence which represents the data being sent, see OOK Modulation
In the car a receiver picks up the signal, then demodulates it to retrieve the data sequence which is processed in a microcontroller. Garage doors and wireless remote controlled mains sockets often use the same system.
By limiting the transmitted power and/or required signal noise ratio the range at which this works can be limited so you can only unlock the car when it is nearby.
To make things more secure the data being send should not be the same each time, there are solutions for this like time changing codes etc.
In a more secure system the key could also house a receiver so two communication over RF with the car can take place.
But anyway: despite what you thought RF signals is what is used.
answered 3 hours ago
Bimpelrekkie
42.1k23790
answered 3 hours ago
Bimpelrekkie
42.1k23790
answered 3 hours ago
Bimpelrekkie
42.1k23790
answered 3 hours ago
Bimpelrekkie
42.1k23790
42.1k23790
3
The OP described the situation of a car needing to know "where" the key is, and not just if it is "nearby." Not locking the car door when the keys are inside vs outside?
– user2913869
3 hours ago
1
See the other answer, if you have enough antennas you can translate "nearby" into "where". OP was asking more questions that just the inside vs outside question.
– Bimpelrekkie
3 hours ago
add a comment |Â
3
The OP described the situation of a car needing to know "where" the key is, and not just if it is "nearby." Not locking the car door when the keys are inside vs outside?
– user2913869
3 hours ago
1
See the other answer, if you have enough antennas you can translate "nearby" into "where". OP was asking more questions that just the inside vs outside question.
– Bimpelrekkie
3 hours ago
3
3
The OP described the situation of a car needing to know "where" the key is, and not just if it is "nearby." Not locking the car door when the keys are inside vs outside?
– user2913869
3 hours ago
The OP described the situation of a car needing to know "where" the key is, and not just if it is "nearby." Not locking the car door when the keys are inside vs outside?
– user2913869
3 hours ago
1
1
See the other answer, if you have enough antennas you can translate "nearby" into "where". OP was asking more questions that just the inside vs outside question.
– Bimpelrekkie
3 hours ago
See the other answer, if you have enough antennas you can translate "nearby" into "where". OP was asking more questions that just the inside vs outside question.
– Bimpelrekkie
3 hours ago
add a comment |Â
Yu Zhou is a new contributor. Be nice, and check out our Code of Conduct.
Yu Zhou is a new contributor. Be nice, and check out our Code of Conduct.
Yu Zhou is a new contributor. Be nice, and check out our Code of Conduct.
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1
It is definitely RF. Don't forget a low frequency signal can be modulated on RF, so you assumption about nanoseconds does not hold.
– Eugene Sh.
4 hours ago
I have that for my car too, and I have been wondering the same. First thing I noticed is that it isn't that accurate. Sometimes, when I'm close to the door, it thinks the key is inside (which is annoying BTW). Then, what I know is that there are multiple antennas distributed at different locations in the vehicle (I don't quite remember if it's two or three). But then, I don't know the definitive answer. Maybe it is just a measure of the signal strength.
– dim
3 hours ago
I am more interested how the "walk-away" feature is working. This one is making me thing that the key has to repeatedly transmit, which is not going well with the battery lifetime.
– Eugene Sh.
3 hours ago
@Eugene Sh. The fobs presumably transmit only when a button is pressed or in response to a ping from the car, so the fob will only transmit when within range of the car, and then only when polled. Presumably the system could poll more frequently at some times than others to optimize response time vs battery life.
– ajb
2 hours ago