To add to the above, GE requires special "add-on"/"companion" switches (so do all the equivalent Jasco products, and so does HomeSeer). Zooz requires "dumb" switches, but some require rewiring the dumb switch and some (with other tradeoffs) need it wired as usual. The current (v2, or Red/Black) generation of Inovelli can actually work in either of these configurations *or* with another smart switch (all with certain benefits and drawbacks)--they designed the product from scratch and tried to accommodate as many different wishes as possible. :) In all cases, the idea is that it depends on the brand and model--it's not the same for all (though Lutron is probably the oddest of the bunch here).