✓ BUILT, TESTED & USED IN MY HOME
Real automations. Real homes. Real-world results.

Why I built this

I wanted my house to react to temperature changes without manually switching the thermostats between heating and cooling. I already had a contact sensor on an exterior garage door, and that sensor reports temperature as well as whether the door is open.

How my equipment works together

Garage contact sensor → SmartThings hub → Alexa → ecobee thermostats. The sensor's temperature is available to Alexa through the SmartThings integration. It is the temperature at the garage sensor, not necessarily the outdoor air temperature or an internet weather forecast. I originally thought a Ring camera supplied the reading; after checking my configuration, I confirmed it is the contact sensor.

Separate routines for warm and cold conditions

I have separate Alexa routines for temperatures crossing warm and cold thresholds. When the garage sensor reaches a configured warm threshold—for example, 75°F—the cooling routine adjusts the ecobees' cooling setpoints. A separate cold-weather routine raises the heating setpoints when its threshold is reached.

All four ecobees are left in Auto mode; Alexa changes setpoints rather than switching the thermostats between Heat and Cool. The thermostat itself decides whether to run equipment based on indoor temperature, setpoints, and its operating settings. An outdoor or garage temperature trigger does not by itself guarantee the AC or heat immediately starts.

Three thermostats participate; the guest house does not

Three ecobees serve my main house and are included in these routines. The fourth serves our guest house and is intentionally excluded—my in-laws prefer their own temperature control. Connecting a device to Alexa does not mean it has to be included in every routine.

The loft gets its own settings

Two main-house thermostats use similar adjustments, around 2°F for cooling. Our upstairs loft gets hotter faster, so its cooling adjustment is larger—approximately 4°F, pending verification. The loft also receives a higher heating setpoint than the two downstairs zones in colder weather. I haven't verified the exact heating offset yet, so I won't invent one.

How to build a similar setup

  1. Choose a contact sensor that actually reports temperature, and pair it with a compatible SmartThings hub.
  2. Confirm SmartThings displays a temperature reading for that sensor, and that the SmartThings–Alexa integration exposes it as a usable routine trigger on your account.
  3. Connect your compatible ecobee thermostats to Alexa and verify which thermostat actions are available.
  4. Set up separate temperature-triggered routines for warm and cold conditions, if your Alexa app supports those triggers and thermostat actions.
  5. Assign the intended heating or cooling setpoints to each participating zone. Give hotter upstairs areas their own settings as appropriate; leave independently managed areas out.
  6. Keep the ecobees in Auto mode only if your equipment and thermostat configuration support the desired heat/cool setpoints and minimum separation.
  7. Test each threshold, verify the correct sensor and thermostat actions, and watch for competing schedules or routines that might overwrite setpoints.
Important: Alexa, SmartThings, sensor, and ecobee features vary by model, software, and integration. This is my working configuration, not a guarantee every device supports the same trigger or action. A garage sensor may read warmer or cooler than the actual outdoors. Avoid rapid or conflicting HVAC changes and follow your equipment's recommended settings.

How this relates to my Bedtime routine

When I say “Alexa, Bedtime,” another routine prepares the house—TVs, lights, locks, and bedroom comfort. These separate temperature-based routines handle the changing seasonal conditions. They are not one giant routine.

Read my Alexa, Bedtime! routine → · Creative uses for contact sensors →

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