GE 45610WB GE Z-Wave Add On Auxiliary Switch - Manual (Page 5)

IMPORTANT NOTE ABOUT 3-WAY CIRCUITS
The term “3-way circuit” refers to a circuit with two switches
and one load (light) like you find at the top and bottom of a
stairway. There are many ways to physically wire a 3-way
circuit and it is important to understand how the circuit you
wish to upgrade to Z-Wave control is wired. Below is a
description of a typical 3-way circuit.
One of the ways to wire a two-switch/one-load circuit is
to route the incoming power through the first switch, then
to the second switch and then to the load. Although very
common and by no means a standard, it is the easiest to
convert to Z-Wave control. With this type of circuit, Switch
1 is replaced by the Z-Wave auxiliary switch and Switch 2
is replaced with the primary Z-Wave switch. The auxiliary
switch does not actually control the power; instead, it sends
a momentary voltage signal through the traveler wire to the
primary switch which in turn, controls the power to the load.