Have a hard time hearing when guests arrive because you just can't hear them knocking? Change all that with the Knock Knock Wireless Door Chime. This sensor and receiver set automatically chimes when someone is knocking at your door, alerting you to their arrival. To use, simply attach the sensor to the door using either double sided tape or screws. The sensor will then activate whenever it feels a knocking vibration. The receiver, which has a 100ft connectivity, will then chime in order to alert you to guests! Now you'll never miss another visitor, even if you're all the way in the back of your home or office.