The wireless pet doorbell is an ideal unit to alert you by music when someone is visiting you or train the dog/cat. With wireless plug-in receiver and battery powered transmitter, it is easy to install and move. The doorbell features 58 ringtones and 5 volume levels to suit your needs, and can reach up to 300m barrier-free wireless distance. Using learning code for pairing, you can add more extra receivers or transmitters to expand this alert system to meet your different requirements.