The RK-1 [Babel] motion sensing module attaches to a cameraphone and turns it into a security monitoring device.
The module senses when someone enters an area, then triggers the phone’s camera and sends the image to an email address of your choice. It looks as though there’s also a heat sensing version available or coming which can sense a human body up to 5 meters away.
More here [Japanese PDF]. It is priced at around $150.00, but only works with a limited number of Japanese handsets at the moment.