x10.com has some simple and relatively cheap security systems and wireless camera rigs (be aware that the latter run in the 2.4 GHz junk band, so if you have a 2.4 GHz phone, you may get beating in the picture). The security systems are easy to set up--basic kit comes with some door/window sensors a motion sensor, and a wireless key fob and control module to turn the system on and off. Makes a loud noise and flashes light. The web site sucks tho.mithuth said:auto on/motion sensor camera mounted inside the garage 9along hte back wall) facing the door so you can catch thier faces if they come back.
If you want something cheaper, I found a really simple motion sensor alarm at lowest--four buttons, you encode a key, and use that to arm and disarm.