Originally Posted by Hans
The reason it would not work is because even a tweeter can generally only go to 10,000-50,000hz where as most keyless entry remotes are in the megahertz or 1,000,000hz range I believe.
I could be wrong but I thought that was the reason.
even if the speaker could produce the frequency necessary, I thought digital cell phones use some compression algorithm so they chop the highs and lows off the microphone signal....
Speakers produce sound waves, whereas radio transmitters (such as keyless entry remotes) produce radio waves. Even if you had a radio transmitter that was operating at 5,000Hz, you wouldn't be able to hear it. Sound waves and radio waves are two entirely
Even if the wireless key fobs produced audio waves (which they don't), a cell phone wouldn't be able to transmit them. Cell phones transmit only audible frequencies of sound waves, usually within the band of about 500Hz to 3400Hz. Modern digital phones compress the sounds using something known as a vocoder to reduce the data rate to something reasonable; the result is a phone that is reasonably good at reproducing human speech and not so good at reproducing other noises. Even if the key fob transmitted sound waves within the cell phone'* audio passband, the vocoder would severely distort the signal.
For the record, it appears that GM keyless remotes operate around 319MHz.
Here'* a pragmatic proof that this won't work: If your keyless entry remote transmitted sound waves at a frequency that a cell phone could transmit, you would certainly be able to hear the transmission. Pick up your key fob and press the buttons. Do you hear anything? No.