Nest Thermostat Generation 3
The Nest Thermostat is probably the most well known Smart Thermostat on the market.
This device comes from the team that developed the iPod. Google since acquired the team and are now developing a number of smart home devices. There are 3 versions of this thermostat and there is some tricky install requirements that can catch you out when purchasing.
Nest Thermostat E
The Nest Thermostat E is the basically the nest thermostat with out the digital display. The result its a more minimal design and a device that required less power to operate.
This is the basic model of the nest thermostat show above. less fancy