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 Any, First, or Last 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.

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

YAML sometimes provides additional options for more complex use cases that are not available through the UI.

Targets

This trigger supports targets. A target tells Home Assistant what the trigger should watch. You can point it at 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, and Home Assistant watches every matching air_quality entity behind that target.

• Entity: one specific air_quality entity, such as air_quality.living_room.
• Device: every air_quality entity that belongs to a device.
• Area: every air_quality entity in a room or area.
• Floor: every air_quality entity on a floor.
• Label: every air_quality entity that shares a label.

You can also mix target types in one trigger. For example, combine a specific entity with an area to watch both at once.

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:

• Any (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 all targeted entities have reset 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.
• Last: 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, then change the state of the targeted entity to watch the trigger fire on your actual entitiesAn 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].

More examples

Real scenarios where this trigger fires in automations and scripts. Copy any example and adapt it to your setup.

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: Any
• For at least: 00:00:00
• Action: Send a mobile notification

alias: "Notify on kitchen gas detection"
triggers:
  - trigger: air_quality.gas_detected
    target:
      entity_id: binary_sensor.kitchen_gas
    options:
      behavior: any
      for: "00:00:00"
actions:
  - action: notify.mobile_app_phone
    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: Any
• For at least: 00:00:30
• Action: Valve: Close

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

Still stuck?

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

These triggers work well alongside this one:

• Gas cleared - Triggers after one or more gas sensors stop detecting gas.