Carbon monoxide level changed

The Carbon monoxide level changed trigger fires after the carbon monoxide (CO) reading on one or more air quality sensors changes by a meaningful amount. Carbon monoxide is a colorless, odorless gas produced by incomplete combustion of fuels like gas, oil, wood, and charcoal. A faulty furnace, a blocked chimney, or a car left running in an attached garage all release CO without any visible warning. Even small increases in CO levels indoors deserve your attention, because prolonged exposure is dangerous.

Imagine getting an instant phone alert the moment your garage CO sensor picks up a shift, giving you time to ventilate before the situation becomes serious. Use this trigger to kick off a ventilation routine, send a safety notification, or log concentration changes whenever your CO sensor reports a significant shift.

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 air quality sensor is in (like your living room or bedroom). You can also select a floor, a device, a specific entity, or a label.
5. From the triggers shown for that target, select Carbon monoxide level changed.
6. Under Threshold type, set how much the level has to change before the trigger fires.
7. 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.co_changed. A basic example looks like this:

trigger: air_quality.co_changed
target:
  entity_id: sensor.living_room_co
options:
  threshold: 5

This fires whenever the living room CO sensor reading changes by at least 5 ppm.

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.

Good to know

• Carbon monoxide is produced by gas stoves, fireplaces, furnaces, and running vehicles in attached garages. A sudden rise in CO is a safety concern.
• The trigger fires on any change that meets the threshold, whether the level goes up or down.
• To react only when CO crosses a specific level in one direction, use Carbon monoxide level crossed threshold instead.

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: alert when CO rises in the garage

Maybe someone left the car idling or the workshop heater is acting up. This automation sends a notification to your phone whenever the carbon monoxide level in the garage shifts noticeably, so you know to open the garage door or investigate the source right away.

• Trigger: Carbon monoxide level changed
• Target: Garage CO sensor
• Threshold type: 10
• Action: Notify mobile app

alias: "Alert on garage CO change"
triggers:
  - trigger: air_quality.co_changed
    target:
      entity_id: sensor.garage_co
    options:
      threshold: 10
actions:
  - action: notify.mobile_app_phone
    data:
      title: "Carbon monoxide change"
      message: "CO level in the garage changed significantly. Check ventilation."

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:

• Carbon monoxide level crossed threshold - Triggers after one or more carbon monoxide levels cross a threshold.