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Honeywell Home Thermostat Model Number RTH221B1039 in the RTH221 Series is a programmable thermostat with a rectangular, wall-mounted design. It has a temperature sensor to accurately control heating and air conditioning systems. The thermostat can be programmed to choose the temperature setting for any day of the week with the push button control style. It runs on two AAA batteries and uses low voltage of 24V. The system switching feature controls Heat, Cool, or Off and the display shows the set temperature. Smart Home Protocol is Thread and programmability makes it easy to use.