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Alabang BRZ I hear what you're saying; you'd need some way to detect the radio from the key fob, only thing is the key fob doesn't broadcast unless the button is pressed.
Question was asked on another forum "How can I detect the signal from a key fob?"
http://www.nerdkits.com/forum/thread/2133/
And the short answer is a 315 mHz +/- 2.5 mHz detector, etc.