Kit makes a light activated chime when a visitor or intruder comes through the door and breaks the light beam. Set it up in a doorway or entranceway. When someone enters the doorway and blocks the light for a second, it will activate a chime in the speaker to let you know someone has come in. Many uses in stores, garages or workshops. It could even be mounted remotely, garage or driveway etc, and have the speaker in the house so you will know when someone comes in. 
 

Kit comes with complete with circuit board, components,  instructions. Operates on 4.5 volts or 3 1.5 volt AAA or AA batteries. Requires basic soldering skills and a 15 to 30 watt soldering iron. Solder is included

Another great kit to have fun with from Bakatronics

Have fun, that's what it's all about.