Always be sure that your door is closed and locked. The Nuki Door Sensor can be easily installed on the inside of your door without drilling or screws. In combination with the Nuki Smart Lock 3.0 (Pro) and the free Nuki app, you can also ensure from a distance that your door is closed and securely locked. You will be notified if your door has been left open longer than usual or if the door sensor detects any movement of the door. With its built-in tamper detection, the Nuki Door Sensor provides maximum security for your home.