Great Smart Thermostat. Requires a 'C' wire for power. Caution when buying EXTRA remote room sensors to make sure they are Series 3 or 4 to be compatible with the Smart thermostat, you can only read the series # by opening the package, opening the battery compartment, and looking at the tiny circuit board for a teeny tiny 3 or 4 that is rotated 90 degrees from the other numbers. If a "1" (or 2 I think), they may note link to the smart thermostat unfortunately. If they link, they work GREAT to allow the Smart thermostat to average the room temperatures then apply that to your heat of cool settings. I highly recommend the the thermostat and remote room sensors (the more the merrier).
I have a schedule set for the times I want my AC/heater to start. The T9 starts them 30-45 mins before the time. This morning the heat came on at 3:08am instead of 4:45am. It has a mind of its own. I just my thermostat to run according to my requests, not when it wants to...