Alarm.com's cost-reduced current thermostat, and the only one in the range that speaks Z-Wave Long Range as well as mesh. Z-Wave Plus with S2 and SmartStart, so Home Assistant drives it locally through Z-Wave JS.
Same 3 heat and 2 cool stages as the ADC-T40K-HD, with humidification, dehumidification, and ventilation handled through a single flexible Z terminal rather than dedicated outputs. The display is a monochrome capacitive touch panel instead of the HD colour screen, which is most of the price difference.
It is the one Alarm.com thermostat that will run without a C-wire, on 4 AA cells. Wire the C anyway where the system has one: on batteries it sleeps, so setpoint changes queue rather than apply instantly.
Do not count it as a repeater either way. Alarm.com’s data sheet is explicit that the T25 never acts as a Z-Wave repeater, mains powered or not, which is unusual for a wired thermostat and worth knowing before you plan a mesh around one.
Z-Wave Long Range is the interesting part. Where a house has an 800-series controller and a thermostat at the far end of a detached wing, the T25 can join as a Long Range node on a direct link to the controller rather than depending on a chain of repeaters. It is a choice made at inclusion, so decide before pairing.
Home Assistant reaches it through Z-Wave JS command classes. There is no zwave-js device file for it yet, so manufacturer configuration parameters appear unnamed; run the thermostat’s own wire detection and setup wizard first and the defaults will be correct.
An ADC-S40-T remote sensor can be paired to it for room-level averaging, though that pairing is an Alarm.com platform feature rather than something the thermostat does on its own.
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