Gas detected

The Gas detected trigger fires the moment a gas sensor entityAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more] starts detecting gas in your home, whether it is a natural gas leak near the stove or a combustible gas buildup in the basement. A gas leak is one of those situations where every second of early warning matters. With this trigger, Home Assistant alerts you instantly so you and your family have time to react, even in the middle of the night or while you are away from home.

Using this trigger from the user interface

If you prefer building automations visually, Home Assistant walks you through this trigger step by step. You pick what to watch, tweak a few options, and save. No YAML knowledge required.

To use this trigger in an automation:

1. Go to Settings > Automations & scenes.
2. Open an existing automation, or select Create automation > Create new automation.
3. In the When section, select Add trigger.
4. Select what you want to monitor. Under By target (see Targets), pick the area your gas sensor is in (like your kitchen or garage). You can also select a floor, a device, a specific entity, or a label.
5. From the triggers shown for that target, select Gas detected.
6. Under Trigger when (see Behavior), pick Each, First, or All to control how the trigger behaves when multiple sensors are targeted.
7. Under For at least, set how long the sensor must stay in the detected state before the trigger fires. Leave it at zero to fire immediately.
8. Select Save.

Options in the UI

Using this trigger in YAML

If you work directly in YAML, or you want to know exactly what Home Assistant does under the hood, this section has the technical reference. It lists the field names you use in YAML, their types, and which ones are required. For how an automation is built in YAML, refer to Automations in YAML.

In YAML, put the settings that are specific to this trigger under options. Keep target, if the trigger uses one, and general settings such as id, alias, enabled, and variables at the top level, next to trigger.

When this trigger starts an automation, it passes data about what happened to the automation. You can use this trigger data in the templates of your conditions and actions. To see which data is available, refer to Trigger data in templates.

In YAML, refer to this trigger as air_quality.gas_detected. A basic example looks like this:

trigger: air_quality.gas_detected
target:
  entity_id: binary_sensor.kitchen_gas

This fires every time binary_sensor.kitchen_gas transitions to the detected state.

Options in YAML

Targets of the trigger

This trigger requires a target. The target is the object that Home Assistant will watch. You can select a single entityAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more], a device, an area, a floor, or a label as a target, and Home Assistant will watch every matching gas detector behind that target.

• Entity: one specific gas detector, such as binary_sensor.kitchen_gas.
• Device: every gas detector that belongs to a device.
• Area: every gas detector in a room or area.
• Floor: every gas detector on a floor.
• Label: every gas detector that shares a label.

You can also select different target types in one trigger. For example, you can add a specific entity and an area as targets in the same trigger to monitor both of them at once.

To learn which entities Home Assistant includes for a device, area, floor, or label, and how it handles several entities, refer to Automation targets.

Trigger variables

When the trigger reacts, the trigger variable identifies the entity that made it react. This is useful when a target contains multiple entities, such as a device, area, floor, or label.

The following trigger-specific variables are available:

• trigger.entity_id: Entity ID of the entity that made the trigger react.
• trigger.from_state: Previous state object of that entity.
• trigger.to_state: New state object of that entity.
• trigger.for: Timedelta object of how long the trigger criteria were met, if applicable.

For example, use {{ trigger.to_state.name }} in an action to include the name of the entity that made the trigger react in a notification.

The trigger variable describes the entity that made the trigger react. It doesn’t contain all the entities of the target.

Behavior with multiple targets

When you target more than one entity (or select an area, floor, or label that contains several), the Trigger when option controls how the trigger responds:

• Each (default): the trigger fires every time any one of the targeted entities transitions. For example, if you monitor three motion sensors in the living room and someone walks past sensor 1, the automation fires. When they walk past sensor 2 a moment later, it fires again. Every individual event counts.
• First: the trigger fires only on the first transition in the targeted group, then waits until none of the targeted entities is in that state anymore before it fires again. For example, if you monitor the same three motion sensors, the automation fires when the first one picks up movement (someone entered the room). The other two firing afterward are ignored, so you get one notification per “someone walked in” event instead of three.
• All: the trigger fires only after the last targeted entity in the group has fired, meaning all of them are now in the expected state. For example, if you monitor the lights in the living room, bedroom, and hallway, the automation fires only once all three have turned off. This is useful for scenarios like “start the robot vacuum only after every light on the floor is off,” so you know the room is truly empty.

Good to know

• The trigger only fires when a sensor transitions from a known, valid state. If a sensor comes back from being unavailable (unavailable) or having an unknown state (unknown), the trigger does not fire for that recovery.
• Use the For at least option to avoid false alarms from brief sensor spikes. Setting a short delay (like one or two minutes) helps confirm the reading is genuine.
• To react to the opposite transition, use Gas cleared.

Try it yourself

Ready to test this? Go to Settings > Automations & scenes, create a new automation, and add this trigger. Save the automation, and then make the trigger react. For example, change the state of the targeted entityAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more], turn on a light that the trigger monitors, or change its brightness. To check whether the automation ran, open its traces.

More examples

Real scenarios where this trigger fires in automations and scripts. Copy any example and adapt it to your setup. In the visual editor, select the UI options listed in the example when they are available, or paste the YAML code.

Automation: get an urgent phone alert the moment gas is detected in the kitchen

Imagine you are upstairs or out running errands and a burner valve is leaking in the kitchen. This automation sends an urgent notification straight to your phone the instant your kitchen gas sensor picks something up, giving you the earliest possible warning to take action.

• Trigger: Gas detected
  • Target: Kitchen gas sensor
  • Trigger when: Each
  • For at least: 00:00:00
• Action: Send a notification message
  • Target: My Device (notify.my_device)

alias: "Notify on kitchen gas detection"
triggers:
  - trigger: air_quality.gas_detected
    target:
      entity_id: binary_sensor.kitchen_gas
    options:
      behavior: each
      for: "00:00:00"
actions:
  - action: notify.send_message
    target:
      entity_id: notify.my_device
    data:
      message: "Gas detected in the kitchen!"
      title: "Gas alert"

Automation: automatically shut off the gas valve to protect your home

When a gas leak happens while everyone is asleep or nobody is home, you want the house to protect itself. This automation watches every gas sensor in the house and, after a confirmed 30-second reading, shuts off the main gas valve automatically. That extra layer of safety means you never have to rely on being awake and nearby to prevent a dangerous situation.

• Trigger: Gas detected
• Target: All gas sensors (by label)
• Trigger when: Each
• For at least: 00:00:30
• Action: Close valve

alias: "Shut gas valve on detection"
triggers:
  - trigger: air_quality.gas_detected
    target:
      label_id: gas_sensors
    options:
      behavior: each
      for: "00:00:30"
actions:
  - action: valve.close_valve
    target:
      entity_id: valve.gas_main

Still stuck?

To find out why the trigger didn’t react, make the change that it should react to, and then open the traces of the automation. If the automation didn’t run, there’s usually no trace, but some triggers record a Did not trigger trace. For details, refer to Testing automations. For common problems and their solutions, refer to Troubleshooting automations.

If that doesn’t help, the Home Assistant community is quick to help: join Discord for real-time chat, post on the community forum with the trigger you’re using and what you expected to happen, or share on our subreddit /r/homeassistant.

Related triggers

Explore related triggers:

• Gas cleared: Triggers when one or more gas sensors stop detecting gas.