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Use the door or window’s Home Assistant binary-sensor entity as the automation trigger. For an instant warning, trigger when its state changes to on and send a Companion app notification to the intended phone. For a left-open reminder, create a second trigger for on with a for duration. Check the entity’s real states first, because unknown and unavailable are not the same as closed.
What a reliable door-sensor alert actually does
A dependable setup separates three situations that are often confused:
- An opening event: the binary sensor changes from its normal closed state to
on. This should produce an immediate notification. - A sustained open state: the sensor remains
onfor a chosen period. This needs a separate reminder trigger usingfor. - A sensor health problem: the entity becomes
unknownorunavailable. This is neither open nor closed and should be handled as a diagnostic condition.
Home Assistant binary sensors store on and off. Their device class controls the labels shown in the interface, such as Open and Closed. The underlying state is what the automation evaluates. See the Home Assistant binary sensor documentation for the state and device-class model.
An automation trigger reacts to a change at a point in time; it does not continuously fire while a condition remains true. Consequently, a door that stays open does not generate repeated “opened” alerts unless you add a timed reminder. The automation trigger documentation describes this state-change behavior.
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Before creating the automation
Confirm the exact entity
Open the sensor’s details in Home Assistant and record its entity ID. A device may expose more than one entity, and the name shown on a dashboard is not necessarily the ID used by an automation. Confirm which entity changes when you physically open and close the door or window.
Watch the state while testing. A normal contact sensor should move between on and off, with the device class making those values appear as Open and Closed. If it shows unknown or unavailable, do not configure an alert that interprets that reading as “closed.” Those values indicate that Home Assistant does not currently have a normal binary reading.
Prepare phone delivery
For a phone push, the Home Assistant Companion app must be installed and connected, notifications must be permitted by the phone’s operating system, and the device must expose a notify target. Companion targets use the pattern notify.mobile_app_<device_id>; the exact device ID is installation-specific. The Companion notification guide explains setup and permission requirements.
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Choose the right automation pattern
| Pattern | Trigger | Use it for | Important behavior |
|---|---|---|---|
| Immediate open alert | State changes to on |
“Notify me when a door opens” | Runs once for the transition; it does not repeat while the door remains open. |
| Left-open reminder | State changes to on and remains there for a chosen for duration |
“Alert when a door is left open” | Represents a sustained-open condition and is separate from the immediate alert. |
| Availability diagnostic | State changes to unknown or unavailable |
Sensor connectivity or reporting problems | Does not claim that the opening is physically closed or open. |
Create an immediate “door opened” notification
1. Build a state trigger
Create an automation and choose a state trigger for the confirmed binary-sensor entity. Set the target state to on. A state trigger with no duration fires when the entity changes into that state, which is the appropriate pattern for an immediate opening warning.
In the visual editor, select the sensor entity and set its “to” state to on. If you use YAML, the structure is equivalent to this conceptual example. Replace both values with the IDs from your installation and verify the current syntax in your Home Assistant version:
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trigger:
- platform: state
entity_id: <your_binary_sensor_entity_id>
to: "on"
action:
- service: notify.mobile_app_<your_device_id>
data:
title: "Home Assistant"
message: "<Named door or window> opened"The angle-bracket values are placeholders, not literal entity or service names. A useful message names the opening (“kitchen window,” “back door,” or another label you use) so alerts remain distinguishable when multiple sensors are installed.
2. Select the Companion notify action
Add a notify action that targets the configured Companion app device. Choose the exact mobile-app notify service exposed by your Home Assistant instance. Do not substitute notify.persistent_notification when your requirement is a phone push; that service creates a notice inside Home Assistant’s frontend instead.
3. Save and test the transition
With the automation enabled, close the door, wait for the entity to show its normal closed state, then open it. Confirm all three points:
- The entity changes to
onin Home Assistant. - The automation records a run.
- The intended phone receives a message identifying the correct opening.
If the door was already open when you saved or enabled the automation, no opening transition occurred at that moment, so no immediate notification should be expected. Close it and open it again to create the transition.
Add a reminder for a door left open
Use a separate sustained-state trigger
For a reminder, create another automation (or another trigger/action branch) that targets the same entity, goes to on, and includes a for duration. Home Assistant’s notification documentation demonstrates a 10-minute garage-door example, while a Core integration example uses five minutes for a back door. These are examples, not universal settings: choose a period that fits the location and normal use.
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- platform: state
entity_id: <your_binary_sensor_entity_id>
to: "on"
for: "00:10:00"
action:
- service: notify.mobile_app_<your_device_id>
data:
title: "Door still open"
message: "<Named door or window> has remained open for 10 minutes"Replace 00:10:00 with your chosen interval. A five-minute reminder may suit a frequently used back door; a longer interval may be less intrusive for a garage or workshop. The timer starts when the state enters on and is satisfied only if the entity remains in that state for the full duration.
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This reminder does not replace the immediate alert. If you combine both behaviors, the opening automation warns at once and the sustained-state automation warns later only when the opening has not been corrected.
Understand timer resets
If the contact returns to its closed state before the duration expires, the sustained-open condition is no longer true and the timed trigger does not complete. Opening it again starts a new interval. The reminder therefore describes the current continuous opening, not accumulated open time across several separate openings.
Monitor unknown and unavailable separately
A contact entity that becomes unknown or unavailable is not reporting a normal binary value. Treating either state as closed can create a dangerous false sense of security: Home Assistant may simply have lost a usable reading.
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If sensor availability matters, add a diagnostic automation for those states. Its message should say that the sensor is unavailable or unknown and identify the affected door or window. A separate diagnostic path keeps a connectivity warning distinct from a physical-open warning and lets you decide whether to notify immediately or only after a period of unavailability.
The binary-sensor integration documentation covers these non-normal states and why they differ from on and off: Binary sensor states and device classes.
Phone push versus a persistent Home Assistant notice
| Channel | Where it appears | What it requires | Best use |
|---|---|---|---|
| Companion mobile notification | The selected phone | Companion app setup, a valid notify.mobile_app_<device_id> target, and notification permission |
Immediate attention when someone is away from the Home Assistant interface |
| Persistent frontend notification | Home Assistant’s frontend | A persistent-notification action; the notice remains until dismissed or updated | A visible reminder for people currently using the Home Assistant dashboard |
A persistent notice is supplementary. It remains in Home Assistant until dismissed or updated, but it is not a phone push. The official action reference is Send a persistent notification.
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Add action buttons only when you handle the response safely
Companion notifications can include action buttons. Pressing a button sends an event back to Home Assistant, allowing an automation to react to choices such as acknowledging an alert or starting another workflow. The return path is useful, but it is not guaranteed to produce a response: the Companion app may crash or close before emitting the event.
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If an automation waits for a button response, include a timeout and a fallback branch. After the timeout, send a second notice, perform a safe default action, or record that no response arrived. Never make a safety-critical workflow depend indefinitely on a phone response. See Companion actionable notifications for the event model and its failure caveat.
Test the complete alert path
Test a fresh opening
- Confirm the sensor currently reports its normal closed value.
- Open the door or window and watch the entity change to
on. - Check the automation trace or run history to confirm the trigger fired.
- Verify that the intended phone received the notification and that the message identifies the correct opening.
Test the sustained reminder
- Close the opening so the entity is not already in the timed state.
- Open it again and leave it open longer than the configured
forduration. - Confirm that one reminder arrives after the duration.
- Close the opening and verify that a later reopening starts a new timing period.
Test the non-normal states
Review the entity while the sensor is unavailable or unknown if your installation can produce those states safely. Confirm that any diagnostic automation uses a message describing a reporting problem rather than claiming the door is closed. Do not infer radio range, battery life, delivery latency, or outage resilience from these automation tests; those properties depend on the sensor, network, phone, and installation and are not established by the Home Assistant documentation cited here.
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No alert when the automation was first saved
Check whether the door was already open. A state trigger responds to a transition, so saving an automation while the entity is already on does not create a new trigger event. Close and reopen the door to test the immediate alert.
The automation runs but no phone message arrives
Verify that the action targets the correct Companion notify service, that the app is connected to this Home Assistant instance, and that the phone has granted notification permission. A persistent frontend action will not solve a missing phone permission because it uses a different delivery channel.
The reminder never arrives
Confirm that the entity entered on and stayed there for the entire duration. Any return to the closed state resets the timed condition. Also check that the automation is enabled and that the notify action works independently with a short, immediate test.
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Alerts identify the wrong opening
Inspect the entity ID used by the trigger and the text in the message. Rename entities or messages so each opening has a distinct human-readable name. The notification target controls where the message goes; it does not determine which sensor caused the automation.
A sensor appears closed during a communication problem
Review the raw entity state rather than relying only on a dashboard label. If the state is unknown or unavailable, handle it with a diagnostic alert. Do not map either value to off in a condition intended to represent a physically closed opening.
A practical design for several doors and windows
Repeat the same two-purpose pattern for each opening: one immediate state-change alert and, where useful, one sustained-open reminder. Keep the sensor entity in the trigger and the opening’s name in the message. This makes traces readable and prevents a generic “sensor on” notification from forcing you to identify the location manually.
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Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteUse different reminder intervals when normal behavior differs. A frequently used entry may need a longer grace period to avoid nuisance alerts, while a rarely opened basement window may justify a shorter reminder. The duration is a policy choice; the documented five- and ten-minute examples are starting points, not requirements.
If several people must receive the warning, add each configured Companion target explicitly and test each phone. For people who are already watching a Home Assistant dashboard, a persistent notice can supplement the push message, but it should not be described as mobile delivery.
What this setup can and cannot guarantee
These automations define how Home Assistant interprets a sensor state and how it requests a notification. They do not, by themselves, establish a guaranteed delivery time or operation during every router, internet, Home Assistant, phone, or sensor failure. The documentation supports the trigger semantics, binary-sensor states, Companion permissions, persistent-notification behavior, and actionable-notification caveat; it does not provide claims about radio range, battery life, latency, or outage resilience.
The reliable baseline is therefore explicit: verify the real entity, trigger the immediate transition to on, add a separate for-based reminder when needed, monitor unknown/unavailable independently, and test the actual phone and sensor path.
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