Management of a thermostat's power consumption

An HVAC system comprises a programmable wireless thermostat and a remote receiver unit. The thermostat includes a user interface having one or more displays, user input devices, such as buttons, sliders, or a touch screen, and a backlight. The thermostat may include a proximity sensor, wherein the user interface is controlled based on a user's presence near the thermostat. A thermostat controller enters into a reduced energy consumption mode and switches the user interface to an idle state when the proximity sensor indicates a lack of user proximity for a predetermined duration. When the proximity sensor indicates user proximity, the controller exits the reduced energy consumption mode and switches the user interface to an active state. During the reduced energy consumption mode, the user interface may be concealed when the user interface is in a housing which is transparent when backlit but is opaque otherwise.