If you have already configured the installation via the Home + Control app, the number is available in the application settings: select "Manage my home" and select the room where the thermostat is installed and select the thermostat. Here you will find the serial number (MAC address). Otherwise, follow these steps to retrieve the thermostat's serial number: 1) Disconnect the thermostat from the power supply directly at the electrical panel. 2) Take a small screwdriver and insert it into the hole on the underside of the thermostat. Press gently to remove the front panel of the thermostat. 3) On the back, you will find the serial number that begins with 00:03:50