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 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 switch or light to the sensor and go. * Low-battery Reminder: There is a reminder on APP if the battery level of the sensor is low. Note: After the product is installed with the battery, there is no signal indicator flashing. You need to press and hold the reset button for 6-10 seconds until the signal indicator flashes quickly, and then enter the APP interface to add a bound device. Specifications: Battery model: AAA 1.5V Working voltage: DC3V 21.5 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: -10C~40C 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 * DW2 Sensor(batteries not included)