Cellphones and key fobs

Originally I came across this here: http://www.wsdmag.com/Article/ArticleID/13453/13453.html

Has anyone tried this? I had always assumed cell phones were mp3 like and filtered the ranges they transmit to make the transmission smaller, but if this works I must be wrong. I tried an off of it by attempting to record the key fob with my phone’s voice recorder, that didn’t work.

– IG

:rolleyes: Everything I have read about this, including Snopes, says this is a myth. Key fobs use RF (radio signals) and a cell phone cannot pick up and retransmit a radio signal from an external source.

I am highly skeptical that this person did what he said he did. The author did not describe exactly how he did it (What were the locations of the two phones being used? Which end was he on and who was on the other end? Where was the car in relation to the two phones?) Snopes sez:

To elaborate, the key fob does not emit any sound that you can record, it sends a radio signal. And last, the claim is that you can send the signal from one phone to another, not record it.


Your link doesn’t work, and I can’t use Snopes’ search feature succesfully.

Er… CookingWithGas, your link.

Here’s the Snopes link.

I call BS on the article claiming that it’s been done. Of course, I never tried it, but it just smells bad.

Basic googling is leading me to believe the key fobs use 260-470MHz transmissions of digital unlocking codes. The US frequency appears to be standardized at 315MHz but I’m not 100% sure on that. I’m not an EE but I would guess it would be extremely unlikely that this would ever work like described? What mechanism would explain such behavior?

I suppose an analog cell phone tower with bad filtering that uses a base frequency of 315Mhz or a higher harmonic could accidentally pick up the keyfob digital signals as part of your analog call, effectively modulating the keyfob signals on top of your audio. When transmitted to the other end the car would react to the signal incoming on that frequency and somehow ignore the noise of your call. :dubious:
This would require so much unobtainium, unexplainium and things-just-don’t-work-like-that-anium that it’s not even meaningful to consider which analog cell phone standards use 315Mhz or a harmonic (I can’t think of any) .

Unless someone tries it before 5:00, I’m going to try it when I get home. No use speculating on such an easy experiment. I’m almost certain it won’t work, but there’s no harm in trying

Mmmmmmmm. Braaaaiiiinnnss.

Ok, I know this a borderline zombie thread, but I just wanted to finally report my results. I just tried it last weekend and surprise - surprise it doesn’t work.

We tried three different cars and nothing happened.

I just wanted to make sure you guys could sleep at night.

You win the longest commute on the SDMB award. Damn!