Knock Knock Wireless Door Chime with Vibration Smart SensorFormat: Retail Pkg Age: Platform: N A 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