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 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.
There is a Mac app called iSentry which does what you are asking. It requires a set schedule to work. It saves video or picture to a designated file on your computer and can send email alerts (which works well with the iPhone).
You have to be sure not to set the sensitivity too light, or something like a ceiling fan will constantly set it off.
I've been using the free iVideon (https://www.ivideon.com/), which let's me record unlimited hours of video locally and has all the schedule and motion detection features. One can pay subscription fee to save the video on the cloud, but I didn't really need it. It works on both Mac and PC.
Another excellent CCTV app for Mac is Sighthound Video, but the free version is limited to 1 camera, and costs $60 for 2 camera license.
Another open-source is ContaCam, and while it is for Windows, it works in Mac with a free software called WINE. Only thing I didn't like was that the scheduler was too simple, and I needed more advanced scheduling that iVideon had.