All of the following AVANTEK doorbells with plug-in receivers can be paired with each other: CB-11/CW-11/CB-12/CW-12/CB-21/CW-21/D-3B/D-3W/D-3G/D-3F/D-3C/DB-21 (For orders purchased before 2021, it is best to contact us to inquire whether they can be paired.) NOTE: One doorbell system supports up to 2 transmitters and an unlimited number of receivers EXPAND YOUR DOORBELL SYSTEM: Compatible with AVANTEK plug-in doorbell sets. A simple and convenient receiver add-on to your AVANTEK doorbell system for increased sound coverage. Note: It does not pair with AVANTEK battery-operated doorbell kits (Model: BA-11/WA-11) or other brands 5 VOLUME LEVELS: 115 dB maximum volume ensures even those with hearing problems can hear the bell; when muted, the flashing light still signals the doorbell has been pressed 52 CHIMES TO CHOOSE FROM: 29 mm stereo speaker delivers rich and crisp sound; 5 adjustable volume levels with a maximum setting of 115 dB; press Next or Previous button to easily choose from 52 melodies MEMORY FUNCTION: The receiver unit remembers your last set melody and volume level even after a power outage; no need to punch in your previous settings