The WC180 has over 16K different transmission (privacy) codes. When you pair the transmitter with the receiver, the unit will randomly select one of 16,0000 codes to pair.
Up to 4 transmitters can be paired with a single receiver. However, since there are only 3 different chime tunes on the receiver, it is suggested to pair up to 3 transmitters by selecting different melodies for each transmitter.
Up to 4 receivers can be paired with a single transmitter.