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.
Recipes using this device
Presence Thermostat Setback
Installs a Home Assistant automation that eases your thermostat into an energy-saving preset once everyone has left, and brings it back to a comfort preset the moment someone returns. Add extra occupancy sensors and any one of them counts as home.
Window Open HVAC Pause
Installs a Home Assistant automation that turns the thermostat off when a window is left open, so you are not heating or cooling the street, and turns it back to the mode it was in once every window is shut. Add door sensors and a temperature sensor for the full picture.