I`ve got a Hive thermostat. Nest is another brand. It's fixed to the wall and runs on batteries. There is a wifi gadget (needs a power supply) that it connects to. You can control it manually or through the mobile (I gave the heating a blast from Hong Kong once) It's very useful if you are away a lot and want to heat the home before you come back. It was just a simple job, fitted by the engineer when I had a new boiler a few years ago.