iON Digital Plunger Wireless Door Security Sensor, DSC (Plunger-D) World's smallest concealed burglar alarm contact/transmitter 5 year battery life CR1620 coin cell battery included Works in wood, vinyl, fiberglass and aluminum doors 3/4" in diameter 1" deep with a 7" external antenna Compatible with current DSC, GE, HAI and 2GIG Wireless receivers