[Folkert van Heusden] installed a bunch of cameras in and around his home. Ostensibly this is for watching the kitties from work, but we’re sure the more accepted purpose is for security. He and his wife don’t really want the cameras rolling when they’re at home. So he added a system by the front door with uses a transit pass to turn on and off the security cameras.
The pass is an RFID tag which gets them on the subways, trains, and buses around the Netherlands. To use it with this system he needed an RFID reader. The one he chose is a USB device which enumerates as an HID keyboard. When it detects a valid card it outputs the tag id as a string of characters. [Folkert's] setup uses an eeePC with a broken keyboard to connect to the reader. A perl script monitors the feed from the reader, and verifies each code as it is received. After authentication the script will enable or disable the networked cameras and update the LED readout accordingly. To keep everything hidden he put it in the closet, using a hole (from a doorknob?) as a wire pass-through.