Hacking a PIR RF signal with PIC 12F683

Deepak from Mindfront.net acquired a PIR alarm sensor module which transmitted a digital code over 433 MHz RF to signal an alarm receiver. The problem: he didn’t have the factory receiver. So he set out to sniff the transmitted RF signal using a RCR-433-AS receiver module with the data out fed into an oscilloscope. This allowed him to monitor the digital coded signal pattern and decode it into individual bits.

He took this information and wrote a program for the PIC 12F683 which would read the receiver module’s data output and trigger only when the intended code was received. Source code for this project is available from Mindfront.net under GPL license.

We can imagine some “dangerous” uses for this hack. To pull off an RF signal replay attack it’s theoretically possible to copy the received code pattern then replay in on the appropriate RF frequency using a transmitter module. If your neighbor uses one of these RF PIR sensors in their yard or driveway you could try a 21st century digital version of ringing the doorbell and running from the safety and privacy of your own home.