Possible Interference Between Key Fob Signals and Other Cars?

[DaveC426913]

I came out to my car (a Chrysler) the other day and went to open my doors using my key fob when I noitced that the SUV (not a Chrysler) parked between me and my car flicked its lights. I was about six feet away from the SUV. Every time I pressed my buttons, be it lock, unlock or trunk, this SUV's headlights and signal lights would flicker rapidly several times. (No, it didn't open the SUV's doors.)

I'm not sure if my fob was electronically triggering the SUV's receptors or whether it was a more direct connection, such as the lights were reacting directly to the signal burst from my fob (like an EMP).

Thoughts?

 

[Amaroq Zev]

That is quite interesting...it is possible that the two had the same frequency...but that wouldn't explain why the doors didn't open. Maybe there is multiple frequencies(sp), one for lights, one for the opening of doors..this is vague I know, but just a thought...

 

[chroot]

Your key fob transmits only a minute about of RF energy; there's no way it produces enough power to actually directly affect the relays and other components that are required to turn the headlights on. Also, had it directly affected some circuits, it would have directly affected all circuits, and you'd have windshield wipers and horns blowing and so on, too.

What's much more likely is that the SUV has some kind of sophisticated alarm system, and perceived your nearby key-fob transmission to be some kind of interference. It flashed the lights as a deterrent to any would-be theif who might be trying to trick its keyless-entry system. I've never seen such a feature advertised for an alarm system, but I suppose it would be easy enough to implement, and may exist.

- Warren

 

[chroot]

That is quite interesting...it is possible that the two had the same frequency...but that wouldn't explain why the doors didn't open. Maybe there is multiple frequencies(sp), one for lights, one for the opening of doors..this is vague I know, but just a thought...

Key fobs don't depend on different frequencies to identify themselves -- they depend on digital authentication methods, and generally transmit on just one frequency. The digital transmission includes an identifier indicating which button was pressed.

- Warren

 

[Kurdt]

I'd say you've just gone into the second hand SUV business (just a joke of course kids)

That would be interesting if it was a security feature. I'd have thought that the lights flashing would encourage a thief that was potentially trying to break in by indicating they were having some success.

 

[chroot]

Well, a lot of cars make warning chirps or flash their lights as a warning, before the alarm actually goes off. I was thinking perhaps Dave was observing such a warning.

- Warren

 

[binzing]

It's probably close enough of a frequency that it "notices" and "acknowledges" it. Gotta run into problems with so many cars.

 

[Poop-Loops]

That would be interesting if it was a security feature. I'd have thought that the lights flashing would encourage a thief that was potentially trying to break in by indicating they were having some success.

Haha kind of like in Mastermind?

http://en.wikipedia.org/wiki/Mastermind_(board_game)

 

[NoTime]

When I was going to college, I got in my car and drove off.
It wasn't until a few blocks later that I reached into the glove box to get something and discovered that that it was someone elses car.
Same colors, key worked fine

 

[chroot]

Back in the days of plain ol' non-electronic keys, that was actually pretty common, NoTime. There were only about a dozen different keys for each model of lock, and your key would often open similar cars.

- Warren

 

[jim mcnamara]

The authorization for keyless entry for cars is not trivial simply because there are so many vehicles, all using the same frequency band. There is interference from other keyless entry devices nearby, for example. In some cases harmonics from other transmitters can interfere.

There is encryption, too. No surprise there. A block 64 bit cipher, KeyLoq, is one commonly used algorithm (its a trade name), used for keyless entry systems for homes and automobiles.

This cryptanalysis paper:
http://eprint.iacr.org/2007/055.pdf
is an attempt at breaking the KeyLoq cipher.

 

[NoTime]

Back in the days of plain ol' non-electronic keys, that was actually pretty common, NoTime. There were only about a dozen different keys for each model of lock, and your key would often open similar cars.

- Warren

Yea, I know about the old key problem.
It's just that if I hadn't ended up searching the entire car for the papers I needed for the appointment I was going to I might have driven it around for weeks before I found out.
They were that close a match.
It's not that I just wasn't paying attention.

I wonder if Dave got an electronic key match with an invalid command set.
Otherwise, I might think half the cars in a parking lot might flash if it was just some interference effect.

Then the owner of the SUV might have been nearby playing head games

If there is a billion to one chance of something then its going to happen to 6 people.

 

[DaveC426913]

I should clarfiy:

- it is not a remote keyless entry - it is simply an unlocking mechanism
- there is no possbile way it was a trick, unless the trickster was sitting on my thumb, there's no way they could have known when or how often I pressed the button
- the lights flickered only faintly, but definitely a sustained flicker - very much as if it was reacting to a digital signal several fractions of seconds long
- if the flickering was any sort of warning, it was a pretty pathetic one

 

[DaveC426913]

I might have driven it around for weeks before I found out.

I'd like to have been a fly on the wall for that phone to the police.

Hello, officer? Um. I appear to have stolen a car.