Laptop Alarm is a great, simple and free software which puts an alarm on your laptop. A loud alarm which will sound if anyone removes the A/C Power, the mouse or any USB device.
It will also sounds if the mouse is moved or in case of shutdown or suspend.
Laptop Alarm becomes really useful and even a must-have if you usually are in places with lots of pople and you want to be more relaxed when you go to have a coffee or relax for a while.
Finally, it doesn't need to be installed, just run it and secure your laptop. If anyone try to steal your laptop, a buzz will surprise the robber and will warn everybody around it.