Use a temperature warning with scheduled reminders
For a Home Assistant freezer temperature alert, use an existing temperature sensor to create a warm/not-warm helper, then let the Alert integration handle the notification schedule. This avoids sending a message for every small change in the thermometer reading.
Check the sensor and send a test phone message first. Next, choose when the warning should start and clear. Finally, configure reminders and test them with a virtual switch before relying on the real sensor.
This guide is for a sensor already reporting into Home Assistant. It does not choose or certify freezer hardware. Check your sensor manufacturer’s operating range and installation instructions; a room thermometer is not automatically suitable for a freezer. Do not drill the appliance or route a cable in a way that damages its door seal.
Research method: researched from current Home Assistant documentation and version 2026.9.3 source code on September 23, 2026. The worked example is hypothetical; Tara has not tested this setup on freezer hardware. The cover is an AI-generated illustration.
1. Check the temperature and phone notification
- Find the measured temperature entity. An entity is Home Assistant’s named reading or control. Use the current thermometer reading, not a fridge integration’s target temperature. Note its entity ID and whether it reports °C or °F.
- Look at its history during ordinary use. Check readings with the door closed and during normal cooling cycles. A flat graph alone does not prove fresh reports. Compare it with an independent appliance thermometer before trusting its values.
- Send a harmless phone message. Sign into the Home Assistant Companion app and allow notifications. In Settings > Tools > Actions, choose your
notify.mobile_app_…action and send “Freezer alert setup test.” The expected result is that exact message on the intended phone.
The Companion notification documentation explains the phone setup. The current Tools documentation uses Settings > Tools; older releases call this Developer Tools. If delivery fails, fix the phone notification path before adding temperature logic.
An alert threshold is not a safe storage temperature. The FDA recommends a freezer temperature of 0°F (−18°C). The warmer values below only demonstrate how a warning works. Choose your own warning settings using the appliance guidance and observed behavior. A cleared phone warning does not establish that food is safe.
2. Create the warm-temperature helper
Open Settings > Devices & services > Helpers > Create helper > Threshold. Name it Freezer warm, select the measured-temperature sensor, and use an upper limit only. Leave the lower limit empty; entering both creates a different, range-based rule.
Hysteresis means a gap between switching the warning on and clearing it. For this Celsius example, set Upper limit: −14 and Hysteresis: 2. It switches on above −12°C and off below −16°C. Between those boundaries, it keeps its previous state during uninterrupted operation. The comparisons are strict: exactly −12°C does not start it, and exactly −16°C does not clear it.
On a narrow screen, swipe tables sideways. Keyboard users can focus a table and use the arrow keys.
| Sensor unit | Upper limit / hysteresis | Starts / clears |
|---|---|---|
| °C | −14 / 2 | Above −12°C / below −16°C |
| °F | 6.8 / 3.6 | Above 10.4°F / below 3.2°F |
The Fahrenheit row describes the same temperatures. A temperature difference of 2°C is 3.6°F; it does not get the 32-degree offset used for an absolute temperature. Recheck these settings if you change the source sensor’s displayed unit.
Open the new helper and copy its actual entity ID. The example below assumes binary_sensor.freezer_warm. A binary sensor reports on or off; the dashboard may show different words. See the current threshold implementation for its missing-data and initialization behavior.
3. Add the repeating alert
The built-in Alert integration uses configuration.yaml, not the automation editor. You need access to that file. Home Assistant OS supports editor apps; Container users edit the mounted configuration directory. Follow the configuration-file instructions for your installation and keep a copy before editing.
Add this block. If you already have an alert: section, add freezer_warm: beneath it instead of creating a second top-level alert: key. Replace the helper ID and phone name. Under notifiers, use the phone action name without the notify. prefix.
YAML is the text form of the configuration; keep the indentation. On a phone, swipe the code sideways to read long lines.
alert:
freezer_warm:
name: Check the freezer
entity_id: binary_sensor.freezer_warm
state: "on"
repeat: [10, 30, 60]
skip_first: true
can_acknowledge: true
title: "Freezer temperature warning"
message: "The freezer warning is still active. Check the temperature and door."
notifiers:
- mobile_app_your_phone
Run the configuration check for your installation, fix any error, then restart Home Assistant at a suitable maintenance time. A restart briefly interrupts its routines. Add alert.freezer_warm, the temperature sensor and the warm helper to a dashboard so you can compare them.
All numbers in repeat are minutes. With skip_first: true, the first message waits ten minutes. The next follows 30 minutes later; later reminders are 60 minutes apart. This waits for the helper to stay on, not for every reading to remain above −12°C. The hysteresis band deliberately keeps the warning active while the freezer cools back down.
A worked example: warming, cooling and reminders
Imagine the helper starts off with a −18°C reading. These are invented times to explain the settings, not measured sensor or phone response times. Assume Home Assistant stays running and readings remain available.
| Time and reported reading | Helper | Expected alert behavior |
|---|---|---|
| 2:00 p.m.: −11°C | Turns on | The ten-minute wait begins. |
| 2:04 p.m.: −13°C | Stays on | The wait continues, even though the reading is cooling. |
| 2:10 p.m.: still −13°C | On | First message is scheduled to be sent. |
| 2:40 p.m.: −15°C | Still on | Second message; −15°C has not crossed the clearing boundary. |
| 2:45 p.m.: −17°C | Turns off | The next reminder is cancelled. |
If the reading had reached −17°C at 2:08 p.m., the warning would have cleared before the first message. If it never cleared, the next reminders would be at 3:40, 4:40 and so on. Phone arrival can be later than the send time.
To silence an episode after checking it, use the alert entity’s acknowledgement control or the alert.turn_off action targeting alert.freezer_warm. Its state becomes off while acknowledged; idle means the watched state no longer matches. Neither is a food-safety verdict. Swiping away a phone notification alone does not acknowledge the Home Assistant alert.
4. Test without changing the freezer
Leave the freezer closed and powered. This software-only test checks the delay, reminders and phone route. It does not validate thermometer accuracy or reception through the appliance.
- Create a Toggle helper called Freezer alert test. Leave it off and copy its ID, typically
input_boolean.freezer_alert_test. - Before commissioning this new alert, temporarily replace its
entity_idwith that test-helper ID, setrepeat: [1, 2], and change its message to TEST: freezer notification setup. Keepskip_first: true. Validate and restart. - Turn the test helper on, then off within 30 seconds. Expect no alert message. Turn it on again and leave it on: expect a first message after about one minute and another two minutes later, allowing for phone delivery delay.
- Acknowledge the alert while the test helper stays on. Expect reminders to stop. Turn the helper off, then on again: the next episode should notify after a fresh one-minute wait.
- Turn the test helper off. Restore the real
binary_sensor.freezer_warmID, the original message andrepeat: [10, 30, 60]. Validate and restart. Check the actual temperature and both real entities before considering setup complete. The alert must no longer be watching the test switch.
Record your chosen thresholds, sensor unit and phone recipient somewhere the household can find them. Check the real helper against ordinary temperature history; do not intentionally warm stored food to create a threshold crossing. Retest phone delivery after changing phones or notification permissions.
5. Handle missing readings and maintenance separately
| What you see | What to check | Next step |
|---|---|---|
| Temperature seems warm but helper is off | Actual °C/°F unit, upper-only mode and upper plus hysteresis | Compare the reading with the start boundary, not just the entered upper limit. |
| Helper is on but no phone message | Initial delay, alert acknowledgement, notifier spelling and phone permissions | Repeat the harmless phone action test, then the virtual-switch test. |
| Temperature becomes unknown or unavailable | The source sensor and its integration | Treat this as a monitoring failure. The temperature alert can stop because the helper is no longer on. |
| Reading stays plausible but never updates | That integration’s reporting or availability information | Investigate reporting separately; an unchanged temperature alone does not diagnose a dead sensor. |
| Behavior changes after a restart | Real temperature, helper state and alert state | Recheck monitoring. This example does not preserve the old wait or guarantee a missed warning is replayed. |
The Alert implementation stops an episode when the watched entity leaves the matching state, including when it becomes unknown. That is why this example deliberately omits an “all clear” message. Add a separate unavailable-device notification for the temperature sensor. Missing data needs its own warning.
Notification delays and acknowledgement are not restored across a restart. The Threshold helper also initializes without its earlier state inside the hysteresis band: for example, a previously active warning at −13°C can restart off. Check monitoring after maintenance. If the real reading needs attention, check the freezer immediately even if the software alert is idle. Keep the appliance alarm or another independent warning available. Home Assistant, its sensor path and phone delivery must all be working for this extra warning to help.
For a more immediate reminder about a door left ajar, add the separate door-left-open routine. A door sensor and temperature sensor answer different questions; a closed door does not prove cooling is working.
Frequently asked questions
Can I use a freezer door sensor instead?
A door sensor can warn sooner about a door left open, but it cannot tell you whether a closed freezer is cooling properly. Use temperature monitoring alongside the door warning when you want both checks.
Does acknowledging the alert mean the freezer is cold again?
No. Acknowledgement only silences the current alert episode. Check the appliance and actual temperature. The next episode can notify again after the watched helper leaves on and later returns to on.
Will this keep working through a Home Assistant restart?
It does not preserve the elapsed notification delay or acknowledgement. The threshold helper also loses its previous position within the temperature band. Check the actual temperature and alert state after maintenance; this example does not guarantee restart catch-up.
Does a local sensor make the phone notification local?
No. The sensor connection, Home Assistant rule and phone delivery are separate paths. Standard Companion app push delivery can need internet services. The Local Push documentation describes a separate connection option and its prerequisites. Keep the appliance alarm or another independent warning available.
When planning household reminders, decide who receives them and what they should check. Tara’s home automation kit for coordinated local routines describes that planning and handoff approach.