The Extend-A-Chime Transmitter connects onto the low-voltage screws in the existing hardwired doorbell and sends the wireless transmission to the Extend-A-Chime receiver (sold separately.) 

Any of our wireless door chimes, except as noted below, may be modified by adding the RC3050T (Extend-A-Chime Transmitter).  For example, if you already have a hardwired doorbell and you like the RC3624 Wireless Shelf Chime, wire-in the RC3050T and it will send a wireless signal to your new RC3624 Shelf Chime.   Your new Wireless Shelf Chime came with a wireless push button, but you would not be using it in this example.  Thus, you can keep your existing hardwired push button in place and hear your new wireless chime when it is pushed.

Lamson Home Products has verified that the following WIRED models are NOT compatible with our Carlon Brand Door Bells. These units are the "Musical Record-A-Tune" which requires a micro processor within the circuit board which makes the "Extend-A-Units" continuously ring. Therefore, they are not compatible with RC3500D/RC3030D/RC3200D.

    * DH840E/SS840E
    * DH852E/DH853E
    * SS852E/SS853E
    * DH845E/SS845E
    * SS846E/SS856E

We also found that some of the Broan Product Line of WIRED doorbells are NOT compatible either.

    * RC305/RC305RW
    * RC306