The Honeywell Home ElitePRO S900 is a professional-grade smart thermostat for whole-home comfort, sold here in white under part number THX900W1/U. 3-inch touchscreen you can recolor to suit the room. It fits most residential and light commercial systems: up to 3 stages of heat and 2 of cool on a heat pump, or 2 heat and 2 cool on a conventional system.

That covers gas and oil furnaces, dual fuel, hot water and steam, 2-pipe and 4-pipe fan coils, PTAC units, and radiant floors with a slab sensor. The thermostat is hardwired on 24 VAC and needs a C-wire for steady power. A single configurable terminal (U) drives one IAQ accessory, so you can wire in a humidifier, dehumidifier, or ventilator and run it from the same screen.

The built-in humidity sensor reads indoor RH, and Smart Away eases the setpoint back when you're away. You manage it remotely through the First Alert app, and it works with Amazon Alexa, Google Home, and Apple Home, plus Matter, over dual-band Wi-Fi and Bluetooth. The S900 is ENERGY STAR certified and may qualify for utility rebates.

In the box you get the thermostat plus the white cover plate and J-box adapter (THP2400WH) for mounting to a 2x4 junction box. With no common wire at the thermostat, add the THP9045A2098/U C-wire adapter (sold separately). The same model comes in black as THX900B2/U.

96 in D (133 x 90 x 24 mm). Backed by Honeywell Home's 5-year warranty.