Smart door/window sensor that sends notifications to the corresponding app when the door or window is opened or closed. Recommended for crime prevention measures when you are out or sleeping. Compact size, can also be used in drawers. Comes with adhesive stickers and batteries, ready to use. Unused. *The outer box has some stains, so it is on sale for ¥100 off the regular price. There are currently 3 of the same product. If you buy in bulk, we will sell it for an additional ¥100 off, so please let us know. ・Instant notification to your smartphone when doors or windows open ・Wi-Fi connection compatible ・Compatible with both iOS and Android ・Easy installation, just stick it on, no tools required ・Can be installed with a gap of 15mm or less between the door/window (Example of usage scenarios) ・Crime prevention measures for entrances, back doors, and windows ・Monitoring while you are away ・Checking the entry and exit of children and pets (Size) Large: 57mm (height) x 29mm (width) x 18mm (depth) Small: 31mm (height) x 16mm (width) x 12mm (depth) ~Below is the manual for using the product~ ① Install the dedicated app from the QR code or by searching. ② Connect your smartphone to 2.4GHz Wi-fi and add the security sensor to the app. (Select "Contact Sensor (Wi-Fi)") ③ Remove the battery insulation sheet and long-press the reset button on the top until the blue LED flashes. Follow the instructions in the app to connect the sensor to the network. ④ Wait a moment and change the displayed name as needed. ⑤ Install the sensor so that the protrusions on the sides of the sensor are within 15mm of each other.