VTech IS7121-22 User Manual page 25

Getting started
Installing the doorbell with an existing wired doorbell
4. Using another wire, slide one end of the metal part underneath the metallic plate on
the doorbell, then connect the other end to the Trans terminal of your chime/buzzer
unit of the wired doorbell.
Option 1: Ring the front doorbell of the existing wired doorbell and the IS7121
doorbell simultaneously.
Angle
Adjustment
View View
Right Left
Chime/buzzer of wired doorbell
Rear Trans Front
20
Transformer