Features:* Works without a gateway connection: No gateway required. The sensor is paired with APP eWelink via BT and controlled on APP eWelink via Wi-Fi.* Status sync and history: Worried about opening/closing doors or windows? You can instantly check the status of the house on the APP. You can view the history for the past 3 months.* Know if your home is safe: Sensors send you an instant notification if it detects someone opening your door or window.* Can see who enters the home: Add a SONOFF camera or an unused smartphone and you can not only get an alarm notification when the door is opened, but also see what's going on in your home.* Get smart in action: Wish the hallway lights up when you walk in the door and goes out when you walk out? Simply connect a SONOFF switch or SONOFF lamp to the sensor.*Low battery reminder: If the battery of the sensor is low, there will be a reminder on the APP.Specification:Battery type: AAA 1.5VWorking voltage: DC3V 21.5 battery (not included)Quiescent current: 40uAEmission current: 15mAWi-fi: IEEE 802.11b 2.4GHzOperating System: (Android 4.1 and iOS 9.0 or higher)Installation clearance: <5mmOperating temperature: -10C~40CMaterial: PCPackaging information:Package size: about 9.5*5.6*3cm/3.7*2.2*1.18inchPackage weight: about 45g / 1.59ozpacking list:1* Sonoff DW2 sensor (battery not included)