Bosch Wireless Reed, Radion, RFDW-SM
An internal magnetic reed switch contact
Supervised for low-battery, cover-tamper, and removal from mounting surface tamper conditions.
Operational up to 5 years using a single user replaceable AAA lithium battery
 Dimensions:Transmitter 19.5 mm x 82.55 mm x 12.8 mm(0.76 in x 3.25 in x 0.50 in)
Dimensions:Magnet 18.5 mm x 24.5 mm x 12.5 mm(0.72 in x 0.97 in x 0.49 in)
Power/Voltage: 1.5 VDC
Battery type: AAA Lithium
Battery life: Up to 5 years