AFSCME 3357-HOF'S BLOG

True or False: You Can Unlock your Car with a Cellphone

Wouldn't it be great if you locked your keys in your car, if you could just call home on your cell, and have your spouse play his/her remote signal into the phone, and then via your phone unlock your car? Some people say this works. A video posted at autoblog.com supposedly proves it works.

No no no, says myth-debunking site Snopes.com. Snopes insists that it's false. Read Snopes' take here.

Until I see it for myself, I'm inclined to believe snopes. The higher frequency that you transmit, the more bandwidth you use up. Cellphones have a low-pass filter that block out sounds above 4,000 Hertz. In addition, the analog to digital converter used to digitize the soud on your cellphone probably has a sampling rate below 10,000 hertz. The remote signal is transmitted in the RF, 300 megahertz band. According to the Nyquist-Shannon Sampling Therom, a an analog signal cannot be accurately replicated through digital sampling unless the sampling frequency is twice the signal bandwidth. Oops, my nerd is showing.

Here's a practical reason why this shouldn't work. If you can transmit the signal by cellphone, in theory, you can intercept and record the signal and use it to steal just about any car.