Here's an interesting little device that detects movement and then records video through the standard peephole of your door...
"Did you know that burglars often come right up to the front door of a home and knock to make sure no one is at home before robbing a house? While you're away for work or holiday, your home could be more vulnerable to break-ins. IntelliCorder is a new gadget to help protect your home and family. The IntelliCorder is a motion-activated surveillance system for your front door. Designed to let you see who's on the other side of the door, it can provide security on demand. This patented door system uses a DVR (digital video recorder) and monitoring screen for real-time viewing and recording of anyone approaching your door within 2 meters...