A “helpful” message just appeared on the bulletin board at work. It looks like it started its life as Email Spam, and while my inbox is thankful that the most recent recipients decided to post it instead of sending it on, I remain skeptical as to its advice.
The message claims that if you lock your keys inside of a car, and have a remote locking device and a cell phone handy, instead of having someone drive your spare keys to you, they can just transmit the unlocking signal over the phone. You have to hold the recieving phone less than a foot from the car door for it to work.
I don’t think this would work, since I do see why a phone would transmit any signal given by those locking devices, and even if they did, wouldn’t the signal be mangled enough to be inoperative? But, has anyone actually tried this?
Sounds familiar, may have been a thread on this in the last few months. I think the answer is “B.S.” Remote car locking devices have a complex algorithm of rotating codes to ensure security and prevent a remote from accidentally opening the wrong car. I don’t have a link handy but www.howstuffworks.com has a good writeup on that topic. This doesn’t even begin to address the issue of how could a cell phone possibly broadcast a signal based on DTMF codes it is receiving, it would be on a different frequency, etc., etc., etc.
The phone can do nothing more than transmit sound waves via it’s earpiece/speaker. Radio waves are translated into sound waves…so there is nothing to transmit except sound waves. The actual radio signal the keyfob (unlocking device) can send out is not going to be relayed by the cell phone earpiece/speaker.
From here in the US keyless remotes are at about 315 MHz. US cell phones use about 800 MHz or about 1.9 GHz. So the radios in US phones are not setup to run at the frequencies needed for keyless entry to cars.
This is a confusion with systems such as “OnStar” satellite system that some cars have. If you get locked out, you call the system’s customer service number on any type of phone, give a code to verify who you are and they can unlock your car via the satellite.
Note that such systems, as well as the radio based key-fob systems, have security problems far beyond regular old keys. Just because there’s hi-tech involved doesn’t make it more secure.
If what was claimed was possible, most if not all remote systems operate through the vehicle antenna. I drove a vanpool van that had a remote, a punk broke the antenna off and the remote would only work within 5 feet of the antenna nub. After the antenna was replaced, all worked fine again.