If you often lose your keys, forget taking the trash out, and find yourself locked out of your house, this sensor can help. The WiFi Door Sensor by EPIC-LEGENDS lets you know whether your door is open or closed. Every time someone opens or closes your door, you will receive a push notification on your phone. The sensor uses a wide-angle infrared sensor to detect the difference between light and darkness. When there is no light, it knows that the door is closed. When there is light, it knows that the door is open. The sensor is easy to install, and the installation only takes a few minutes.