The Ecobee 4 is a smart thermostat that includes a second room sensor and it comes with Alexa built in, so you have fast access to voice controls wherever your thermostat is installed.
Unlike Nest and many other thermostats, the Ecobee 4 includes a sensor that you can put in another room. This lets your heating system know when someone is in that room and will keep the heat or A/C running to make sure that room is at the right temperature. It comes with one sensor and you can add others.
The Ecobee 4 has Alexa Voice Services built in so you can control it with your voice and you can also use many other Alexa skills. The thermostat has microphones built in and a speaker so you can even use it to play music.