This week on Systm, the guys over at Revision3 put together a motion activated silly string shooter. They used a common motion flood light to trigger the project. The project also used compressed air and a solenoid to press the silly string can. My only issue with this project, is that I would think you could use electric solenoid to press the can. The hole tank of compressed air to activate the silly string seems like overkill. Also, the tank of air should run out very fast if activated every 5 sec. on Halloween.