Rf motion sensor connected to USB receiver

I am JUST getting into home builds and i want someone that can help me or make one for me.. I want a motion sensor device that can send a signal to a USB receiver.. I then want the usb receiver to inturpert the signal and do something .. - like open or toggle a program on that computer... ultimately it would be a cubical boss alert device.. when it detects motion it automatically flips my application! :) Any takers? Ryan