Features: * Work Without Gateway Connection: No gateway required. The sensor is paired with APP eWelink via BT and is controlled on APP eWelink via Wi-Fi. * Status Sync & History Records: Worry about leaving your door or window open/closed? You can view instantly the status of home on APP. You can check history records over the last 3 months. * Know Whether Home is Safe: The sensor will send you a notification immediately if someone is detected to open your door or window. * Can See Who Come into Home: Add SONOFF Camera or an unused smartphone, and you can view what's going on in your home not just receive the alert notification when the door is open. * Made Smart in the Action: Want the hallway to light up when you walk into the door and light off when you walk out the door? Simply connect the SONOFF switch or SONOFF light to the sensor and go. * Low-battery Reminder: There is a reminder on APP if the battery level of the sensor is low. Specifications: Battery model: AAA 1.5V Working voltage: DC3V 2×1.5 battery (not included) Quiescent current: ≤40uA Emission current: ≤15mA Wi-fi: IEEE 802.11 b 2.4GHz Operating systems: (Android 4.1& iOS 9.0 or higher) Installation gap:＜5mm Working temperature: -10°C~40°C Material: PC Package Information: Package Size: Approx. 9.5*5.6*3cm/3.7*2.2*1.18in Package Weight: Approx. 45g/1.59oz Packing List: 1 * Sonoff DW2 Sensor (batteries not included) * Work Without Gateway Connection: No gateway required. The sensor is paired with APP via BT and is controlled on APP via Wi-Fi. * Status Sync & History Records: Worry about leaving your door or window open/closed? You can view instantly the status of home on APP. You can check history records over the last 3 months. * Know Whether Home is Safe: The sensor will send you a notification immediately if someone is detected to open your door or window. * Can See Who Come into Home: Add SONOFF Camera or an unused smartphone, and you can view what's going on in your home not just receive the alert notification when the door is open. * Made Smart in the Action: Want the hallway to light up when you walk into the door and light off when you walk out the door? Simply connect the SONOFF switch or SONOFF light to the sensor and go.