I recently bought a car that has keyless entry. You walk up to the car singing “I’ve Got Something In My Front Pocket For You,” press the button on the door, and as long as you’ve actually got the key fob in your front pocket, the door will unlock.
Evidently this only works within a very short range: if I’ve got the key fob, I can unlock the door on my side, but my wife can’t unlock the door on her side. Again, this is when using the button on the door; if you use the button on the key fob, you can of course unlock all the doors from several yards away.
So how does the car gauge how far away the key fob is? Is it based on signal strength, or are they doing a time-of-flight calculation on the signal return to make a more definitive distance measurement?
my WAG is that the button on the door is checking for the proximity of the fob via RFID, which has a very short range, while the button on the fob uses whatever fobs normally use, which is usually good from across a small parking lot depending on obstruction and/or battery in my experience.
since this is GQ, I expect someone to come along and correct me thoroughly at any moment.
If it’s a Nissan you can push the door button quickly twice and it will unlock all doors so your wife doesn’t stand in the drizzle or make you reach in your pocket to hit the fob.
This may be the case for other makes. I’m just familiar with Nissans.
My car does it when you touch the door handle . One of the options is unlock drivers door only or all doors, mine is set to all doors. (The default setting was drivers door only). It’s a honda.
My Prius default is driver’s door only, but I’ve reset it to unlock all doors when I touch the handle. It will turn on the interior lights as I approach within a few feet.
On how;
It is / using RFID.
Radio-frequency identification (RFID) is the use of radio-frequency, electromagnetic fields to transfer data, for the purposes of identifying.
The RFID ‘tags’ contain electronically stored information. Most tags are non-powered and read at short ranges (a few meters) via magnetic fields (electromagnetic induction). Others use a local power source such as a battery, or collect energy from the interrogating EM field, and then act as a passive transponder to emit microwaves or UHF radio waves (i.e., electromagnetic radiation at high frequencies).
from : Radio-frequency identification - Wikipedia
When you press the button, the car scans for the tag an opens your door if it detects your car’s tag.
And by the way, RFID is the same basic technology used in many badge-access doors (where you hold the badge near a box next to the door to get access). It’s Near Field Communications (NFC).
It’s also used by some highway toll systems where you drive by a toll area and it automatically recognizes you. And some gas stations use it for pay at the pump. It’s popular with credit card payments in some countries.
And that trick that some cell phones do when they share a picture, video, or contact by touching the backs together? Part of that is done with this technology.
It probably doesn’t. If it receives a recognizable signal (which probably requires the fob to be within a few feet), it opens the door. If not (because fob is too far away, or not the right one for the car), door stays locked.
IIRC, the reason for the different proximities for active versus passive use of the fob is… well, passivity vs. activity. When you hit the button on the fob from say, 20 meters or whatever, you’re actively engaging comms; when you’re just activating via proximity, it’s passive comms (as mentioned up-thread, RFID is the technology used in the badge you use to get into your office… and it would be tough to stuff that in your wallet if it had a 9 volt attached to it).
There is also a security function to this - it’s one thing to be able to open the doors when you’re 30 feet away and within line of sight of the vehicle. Quite another if anyone can start your car and drive off any time you’re within 30 feet of it.
Is it really RFID? I thought they used a proprietary system.
But can the passenger door be opened if the fob is on that side? Maybe it’s a matter of only allowing the driver’s door to unlock, no matter where the fob is.
It could be TOF. At least if the signal from the key takes too long to arrive, the car won’t acknowledge it. 2 years ago, MIT Technology Review published a report (http://www.technologyreview.com/news/422298/car-theft-by-antenna/?a=f) on hacking such cars by extending the wireless signals to where the key was, allowing them to unlock doors, start the engine and drive away. It doesn’t say how far they could extend the range, but it should be in the 10s of meters.
Just to be clear you’re talking about two different systems here. The OP is asking about the newer proximity passive key fob systems, not the older active keyless entry systems. Keyless entry remotes are just (digital) radio transmitters that send a signal to a receiver in your car. They use a fairly sophisticated ‘rolling’ encryption system to prevent thieves from capturing your code. The newer passive fobs are RFID. You have to hit a button on your car (on the outside to unlock it, on the dash to start it) and it then sends out a (again digital) signal which only the right key fob will correctly ‘respond’ to (either actively with a battery or passively as simply an antenna).
As for the OP actual question I would guess that there isn’t any timing system to determine how close you are to the door, it’s simply a matter of the driver’s door’s RFID emitter being (deliberately) very short range.
. One of the options is unlock drivers door only or all doors, mine is set to all doors. (The default setting was drivers door only). It’s a honda.
), and yes, a double-tap results in all doors unlocking.