A thermostat assembly , comprising: a first portion comprising: a power circuit configured to receive power via internal housing line voltage wiring ; a power conversion circuit configured to convert the power received via the line voltage wiring into power at a second voltage level lower than the line voltage; a first connector ; and a second portion , comprising: a second connector configured to removably connect to the first connector and receive power from the first portion at the second voltage level; a temperature sensor configured to measure an ambient temperature of an outside environment; a communication chip configured to communicate wirelessly with a primary heat source ; the thermostat assembly characterised in that the first and second portions are separated by a barrier located in a frame of the first portion; the barrier comprises a dielectric and thermodynamic insulator that inhibits dissipation of heat from the first portion to the second portion to reduce an effect of a temperature of the first portion on the temperature sensor; and the barrier is positioned to prevent a human user from touching any electrical components of the first portion that receive power at the line voltage when the second portion is removed from the first portion. a first portion comprising: a power circuit configured to receive power via internal housing line voltage wiring ; a power conversion circuit configured to convert the power received via the line voltage wiring into power at a second voltage level lower than the line voltage; a first connector ; and a power circuit configured to receive power via internal housing line voltage wiring ; a power conversion circuit configured to convert the power received via the line voltage wiring into power at a second voltage level lower than the line voltage; a first connector ; and a second portion , comprising: a second connector configured to removably connect to the first connector and receive power from the first portion at the second voltage level; a temperature sensor configured to measure an ambient temperature of an outside environment; a communication chip configured to communicate wirelessly with a primary heat source ; the thermostat assembly characterised in that the first and second portions are separated by a barrier located in a frame of the first portion; the barrier comprises a dielectric and thermodynamic insulator that inhibits dissipation of heat from the first portion to the second portion to reduce an effect of a temperature of the first portion on the temperature sensor; and the barrier is positioned to prevent a human user from touching any electrical components of the first portion that receive power at the line voltage when the second portion is removed from the first portion. a second connector configured to removably connect to the first connector and receive power from the first portion at the second voltage level; a temperature sensor configured to measure an ambient temperature of an outside environment; a communication chip configured to communicate wirelessly with a primary heat source ; the thermostat assembly characterised in that the first and second portions are separated by a barrier located in a frame of the first portion; the barrier comprises a dielectric and thermodynamic insulator that inhibits dissipation of heat from the first portion to the second portion to reduce an effect of a temperature of the first portion on the temperature sensor; and the barrier is positioned to prevent a human user from touching any electrical components of the first portion that receive power at the line voltage when the second portion is removed from the first portion. <EOS>