I bought three of these for two houses, connected them to our smartphones, as well as Alexa. We did get one faulty unit. However, we had it replaced in 24 hours with 's "simultaneous return", which was fantastic. I found we didn't need the model with the extra temp sensor.You can talk to Alexa and say things like, "Alexa, what's the temperature upstairs?" or "Alexa, make the temperature 77 degrees downstairs." We still haven't stopped laughing every time we do and she replies that she's done so.Before you choose a unit, pull off your existing thermostat and see if you have a "C" wire (often blue). If not, you'll need to use the (included) power module. I recommend you use one of the spare wires and connect the C wire to your HVAC; it's better than using the power module. Also, use Ecobee's compatibility tool on their web site. Trust me; do that.Wish we had these 10 years ago when people borrowed our vacation home and left the AC on max in the summer when they left, or the heat on full blast in the winter. It has the capability of a passcode on the wall unit, but we haven't had to use that yet.Last thing, you really don't need any technical skill to install this yourself. They make the directions pretty easy to follow; they have online chat; help phone line; and there are tons of YouTube videos by people who bought and installed them.