Motion Detection with iSight/FaceTime Camera

I'd like to use my iSight camera to detect motion, and if any motion is detected, record a short movie (until the motion stops) for security purposes (ok, I want to spy on my cat).

Is there software available to do this? Free/open is preferable.

I've used iAlertU before: takes a screenshot, not a movie, but it is free.

There is also SecuritySpy which does record movies but isn't free.

I am using witness app successfully for 3 months now. It's incredible. If you combine it with the iPhone app, you can even receive the alert when you are on a remote location.
The only bottleneck is that it costs something like 39 USD. But i would definitely recommend it, it works pretty well!

iCam looks like it will work.