Are you in the US or the UK? The terminology is different.
If you’re in the US, then if you have one fixture which is turned on by two different switches, then that is called a “three-way.” If it can be turned on by three different switches, it’s called a “Four way.” Once which will be the “master” and the others will be “auxiliaries.”
If you’re in the UK, the exact same set up, one ceiling fitting turned on by two different switches, is called a “two-way.” And the one that can be turned on by three different switches is called a “three-way.”
UK is doing it the easy way, just counting the number of switches.
The US is actually counting the number of terminals on the switch inside the wall. A normal on/off switch has two terminals. The auxiliary switch which is the extra switch that controls the same light has three terminals hence “three-way switch.”
In the US, there are at least eight different ways to wire this kind of set up. And then once you add Smart Switches there are even a couple of more. But the wiring for Smart switches will be somewhat different than the wiring for a nonnetworked switch because you also have to provide power to the radio that talks to the network. So this is one reason that people get very confused.
If you are using network switches you can either connect the auxiliary to the master with an actual wire, the way a nonnetworked switch pair would work, or with some models you can do what is called a “virtual three-way” which means the auxiliary switch talks wirelessly to the SmartThings hub, which then talks to the master. So the two switches don’t have to be wired together.
All of that is more than what you need to know right now except for two things:
- Most smart switches require a neutral wire in the switchbox. This is not true of dumb switches. So if you want to go with smart switches rather then smart bulbs, you will probably need to check and make sure that you do have a neutral wire in each switch box where you want to use a smart switch.
Two) You can’t mix-and-match switches in a three-way. You generally need to get the auxiliary model that was made to work with exactly thatmaster. So if you are going to replace existing dumb three-way switches you will need to replace both of them.