Does anyone know the details of how the proximity smart key for car works? I'm talking about those systems where you have a wireless key for your car and when you approach the vehicle you press or touch a button on the door and the car will unlock.
It seems that the key is always transmitting a signal and the car is always listening, or vice versa.
I'm more interested in what chips are the keys using and how they achieve so much battery life giving the fact that they are always transmitting, or listening.
I've already checked the subject. I found some low power rf transmitters that have like 8-10mA current consumption when transmitting, which seems like a lot for a key that has the battery changed once a year or a couple of years. Maybe they sent the signal once a couple of seconds. Who knows? These are the details that I want to find out about.
No. It seems that something is transmitting all the time. For example, in my car, when I get near it, the interior lights open up. And this is without me pressing any button.
theace:
I've already checked the subject. I found some low power rf transmitters that have like 8-10mA current consumption when transmitting, which seems like a lot for a key that has the battery changed once a year or a couple of years.
You're looking at it backward. The RFID "transmitter" is in the car, not the key. The transmitter that is in the key is a standard RF transmitter, which is only active when a button on the key (fob) is pressed.
I think there are two parts to the answer to your question - I would suspect that RFID is involved in the "proximity" portion of the question, but the "button press" to unlock involves a transmitter in the key and I would expect that it transmits a different code each time (they call it a rolling code). That way, it makes it very difficult for someone else to capture what your key transmits and make a clone since the code it transmits is not valid the next time. See this link for more information on how that works: Rolling code
I do know that with my new GMC truck, it has to "learn" about any keys that are valid and it identifies them. You have to first have a key made at the dealership, then you have to go through a couple of steps to let the truck synchronize with the new key so it knows it is valid. You have to have at least one recognized key to let it learn about the others. If you lose all the keys, then you have to go through a process of getting a new key made and let the truck "learn" about the new one (which then invalidates all the "lost" keys so nobody else can use them).
Passive RFID in the keyfob, and the car does not transmit continuously. It only has to check every few seconds with a short burst, then only transmit for a second if there is a tag nearby.
At least with mine, there are two parts. There is the key (that apparently has some sort of RFID chip in it because there are NO contacts on the key - just a funny machined groove for the physical "key" part. The fob with the buttons on it is physically separate from the key. I can unlock/lock/start it with the fob (but not drive - only do a remote start to warm it up). Using the physical key, I have to manually unlock the doors and then can use the key (without the fob) to start/drive. I suspect the fob is the part that would be using the rolling code and the key has just a RFID chip in it although some of those also support rolling codes etc.). At least this is what the 2015 GMC truck uses. The key does not have a battery in it, but the fob does (I think it is the usual CR2032 3v battery).
Thanks for the answers. I didn't know about active rfid. I also found that there is an battery assisted passive rfid, although I don't find any diy guide. Everything related is only available as end product.
theace:
Thanks for the answers. I didn't know about active rfid. I also found that there is an battery assisted passive rfid, although I don't find any diy guide. Everything related is only available as end product.
Sounds likely.
Car fobs are encrypted.
They can be hacked with something called a back channel attack,
Although not easy , once done any fob/car from that manufacturer is at risk.
Car manufacturers are mass market and probably do not want the risk of saying too much.
The means exists to do this but is not cheap/practical for small quantity.
doughboy:
it has to be an active component, as the battery needs to be replaced in just a little over a year on a Lexus smart key.
I think it depends on the complexity of the key and what features it has. My car has basic keys with that proximity thing and 3 buttons (lock, unlock, trunk), so this could be battery assisted. Others offer realtime car information like battery, door closed, windows closed, etc. Those might be active.
After checking some specs, I realized that such feature (proximity sensing) can be achieved using bluetooth low energy. Bluetooth enabled in the "key" and bluetooth enabled in the "car". The "car" is in advertising mode; the "key" is scanning (it also works viceversa; the choice is made so the "key" consumes less current). When the "key" sees the "car" it connects to it (pairing previously set up) and they start talking.
BLE scanning uses very small current, <<1mA. BLE advertising also is very low power. The range is around 10 meters, maybe more in open areas, maybe less in crowded spaces.
I used quotes because I was talking about a similar system that I may implement (obviously the car keyless system doesn't use bluetooth).
Using bluetooth is more feasible as the documentation and components are easier to find and widely used.
Thanks for the help on this one!
If no one has anything to add, I think the topic can be closed with the following conclusions:
The keyless car system with proximity feature uses a Battery Assisted Passive RFID or an Active RFID. This allows the key to operate from a year to a couple of years without replacing the battery. A similar diy project is hard to create because the hardware and documents describing hardware and schematics for BAP or Active RFID are scarce, or they come as end products (most of them as keyless systems for cars).