What's in the box:

Door Alarm Sensor Anti-Theft Door Window Alarm Home Security Wireless Magnetic Sensor (Standard)

Features:
Smart door/window sensor real time detects if the door/window is open.
15s quick response, the alarm sounds once door/window is opened.
Smart control the door/window via your smart device.
Just powered by a CR2032 battery, which is low power consumption, and the battery is included.
Super mini size, and its back with double-sided adhesive for easy installing and mounting.
Suitable for door, window, drawer, cabinet, mailbox, etc.

Specifications:
Material: ABS
Power Supply: 1 * CR2032 battery
Working Temperature: -10~45?
Working Humidity: 10~90%RH(non condensing)
Item Size: 44 * 26 * 12mm / 1.73 * 1.02 * 0.47in
Item Weight: 15g / 0.56oz
Package Weight: 26g / 0.94oz
Package Size: 8.2 * 6 * 1.5cm / 3.23 * 2.36 * 0.59in

Package List:
1 * Sensor

Note:
Need to use in combination with smart gateway.