Lifehacker - Motion Detection Is an Effective, Dead Simple Security Camera App - Featured Windows Download
http://lifehacker.com/5233052/motion-detection-is-an-effective-dead-simple-security-camera-app

Motion Detection is a free application that turns your webcam into a motion-sensing security camera in just a few clicks.

Windows only: Motion Detection is a free application that turns your webcam into a motion-sensing security camera in just a few clicks.