[LAU] measuring frequencies and then doing something....

Here's one for ya. I'd like to have a program which "checks" for a certain frequency every 20 minutes or so while I'm not in the room. If this frequency happens (and my microphone picks it up, of course) something happens, I'm thinking something web-like. The function below sucks and I'm aware of that. Just fishing for any ideas. Thanks, amigos! -Aaron $curr_frequency(){ wicked function which listens to the mic every 20 minutes } $frequency = ''; if ($time >= 1200000 ) { //20 minutes curr_frequency (&$curr_frequency, $time); return $frequency; }; if ($frequency == '2500hz') //maybe make this a range { do something neato; } }