ERA-DCKIT-2 
The ERA-DCRX is a four (4) zone receiver meaning each zone will play a distinct sound. You can program / pair as 3 transmitters (such as a push button) to a particular zone as you want (for a overall total of 12), but all the transmitters in that zone will play the melody selected for that zone.
For example, zone 1 may be set to play the "ding-dong" sound. When any transmitter paired to the zone is triggered, the receiver will play the "ding-dong" sound. In this example, I have a push button on the front door paired to zone 1.
For zone 2, I want to program a push button for the back door. When programming, I set that zone to play the Westminster Chime. When that push button is triggered, the receiver will play the Westminster Chime.
This enables you to distinguish a visitor at the front door versus the back door giving you a business alert chime for the front door..