Milesight - 4 * 4000mAh ER18505 Li-SOCl2 Replaceable Batteries Battery Life: Around 3 Years (10 min Interval) Built-in Multiple Sensors Including NH3, H2S, Temperature and Humidity Equipped with Buzzer and LED Indicator to Indicate Threshold Alarms Support Milesight D2D Protocol Damp-proof Coating NFC Enabled