It used to be that we told everybody that you would have to get the specific accessory switch for the specific master model with smart switches, because smart switches are wired differently than dumb switches. That’s to make sure that the radio inside the switch always has power so it can hear the next “on“ command from the network. A lot of dumb switches are wired in a figure 8 pattern where turning on power to one switch cuts the power to the other but that won’t work for smart switches.
Nowadays there are a few models which can be used with an existing dumb accessory switch, including some of the Inovelli and some of the Lutrons, but if you do that, even for those models you can’t do dimming from the dumb accessory. Only on/off.
The GEs, however, do require their own matching accessory switch. But then you will be able to do dimming from the accessory, so that’s a good thing. (Both GE and Honeywell are actually made by Jasco and are the same hardware, although different firmware may give them slightly different features.)
So as always, the first rule of home automation applies: “the model number matters.“
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