GE SmartHome Doorstop Alarm 2 pack special $16.95 + $6.95 shipping @ Zazz today only
deceptively simple, but has a lot of advantages - there's no need to drill holes in anything to install it. It's super-light and easy to pack, so it can go anywhere. And beyond making a noise, it also blocks entry like any other doorstop. So even hearing-impaired intruders are still thwarted!