Here are the most basic sensors of any alarm system. These contact switches for closed circuit systems are ideal for doors, windows, and sliding doors. Measuring 2.48" long and half an inch high, they attach with wood or sheet metal screws (not included) to the frame of the door or window and the case or jam. The switch is waterproof and mounted in a high-impact plastic case. The rhodium plated contacts handles up to 100mA at 100 volts DC and are rated for 50 million openings and closings. It can reliably operate in temperatures between -15F and 160F. The sensor's maximum operational gap is ". Also available for open circuit systems. Mount the magnet on the door or window so that the two are in contact with each other when the door or window is closed. Slotted mounting holes make it easy to adjust the distance between the magnet and the sensor.