Carbon monoxide value

The Carbon monoxide value condition passes when a carbon monoxide (CO) sensor’s reading meets a specific level. Carbon monoxide is a colorless, odorless gas produced by incomplete combustion, and even moderate levels deserve attention. This condition gives you finer control than simpler detected or cleared checks, letting you start ventilation at a lower reading and sound the full alarm only when concentrations climb higher.

Using this condition from the user interface

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

To use Carbon monoxide value in an automation:

1. Go to Settings > Automations & scenes.
2. Open an existing automation, or select Create automation > Create new automation.
3. In the And if section, select Add condition.
4. Select what you want to check. Under By target (see Targets), pick the area your carbon monoxide sensor is in (like your hallway or garage). You can also select a device, a specific entity, or a label.
5. From the conditions shown for that target, select Carbon monoxide value.
6. Under Threshold type, set the level the condition checks against:
   1. Pick whether the reading must be Above, Below, In range, or Outside range of the threshold.
   2. Select Number or Entity:
      • Number: Enter a fixed level directly, for example 35. For In range or Outside range, enter both a lower and upper bound.
      • Entity: Use a sensor entity or a number helper entity as the threshold:
        • Number helper: You can adjust the threshold value without editing the automation. The sensor reading is compared against the number helper’s current value.
        • Sensor: Its current reading becomes the threshold and updates automatically as the sensor changes.
        • For In range or Outside range, you need two entities: one for the lower bound and one for the upper bound (for example, two separate number helpers).
        • If you don’t have a number helper, you can create one by selecting Create a new number helper.
7. Under Unit, select the concentration unit (ppb, ppm, mg/m³, or μg/m³) to use for the threshold comparison.
8. Under Condition passes if (see Behavior), pick Any or All.
9. Select Save.

Options in the UI

Using this condition 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, put the settings that are specific to this condition under options. Keep target, if the condition uses one, and general settings such as alias and enabled at the top level, next to condition.

In YAML, refer to this condition as air_quality.is_co_value. A basic example looks like this:

condition: air_quality.is_co_value
target:
  entity_id: sensor.hallway_co
options:
  threshold:
    type: above
    value:
      number: 35
      unit_of_measurement: "ppm"
  behavior: any

This passes when the hallway CO sensor reads above 35 ppm.

Options in YAML

threshold:
  type: between
  value_min:
    entity: input_number.co_alert_level
  value_max:
    number: 9
    unit_of_measurement: "ppm"

Targets of the condition

This condition requires a target. The target is the object that Home Assistant will check. You can point the condition 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 will evaluate every matching carbon monoxide sensor behind that target.

• Entity: one specific carbon monoxide sensor, such as sensor.hallway_carbon_monoxide.
• Device: every carbon monoxide sensor that belongs to a device.
• Area: every carbon monoxide sensor in a room or area.
• Floor: every carbon monoxide sensor on a floor.
• Label: every carbon monoxide sensor that shares a label.

You can also select different target types in one condition. For example, you can add a specific entity and an area as targets in the same condition to check 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.

Behavior with multiple targets

When you target more than one entity (or select an area, floor, or label that contains several), the Condition passes if option controls how the results combine:

• Any (default): the condition passes if at least one of the targeted entities matches. For example, if you check three smoke sensors and only one of them detects smoke, the condition still passes. This is useful for questions like “is there smoke anywhere in the house?”
• All: the condition passes only when every targeted entity matches. For example, if you check the same three smoke sensors, the condition passes only once all three report cleared. This is useful for “is the entire house safe now?” checks, so your automation does not send an all-clear while one room still has a reading.

Good to know

• Sensors that are unavailable or unknown are skipped. With Any, the condition passes if at least one of the other targeted sensors matches. With All, it passes if all the other targeted sensors match. If all targeted sensors are unavailable or unknown, All passes and Any fails.
• For simple binary detection without a specific threshold, use Carbon monoxide detected or Carbon monoxide cleared.

Try it yourself

Ready to test this? Go to Settings > Automations & scenes, open an automation, and add this condition. Trigger the automation with and without the condition met, and watch whether it continues or stops.

More examples

Real scenarios where this condition gates an automation. Copy any example and adapt it to your setup. In the visual editor, select the UI options listed in the example or paste the YAML code.

Automation: check CO levels when you arrive home

When you pull into the driveway, you want to know if the air inside is safe before settling in. This automation triggers when you enter the home zone and checks the hallway CO reading. If the level is above 20 ppm, you get a notification right away so you know to open the windows or stay outside until the air clears.

• Trigger: Zone entered
  • Target: Frenck
  • Zone: Home
• Condition: Carbon monoxide value
  • Target: Hallway CO sensor
  • Threshold type: Above 20 ppm
  • Condition passes if: Any
• Action: Send a notification message
  • Target: My Device (notify.my_device)

alias: "CO check on arrival home"
triggers:
  - trigger: zone.entered
    target:
      entity_id: person.frenck
    options:
      zone: zone.home
conditions:
  - condition: air_quality.is_co_value
    target:
      entity_id: sensor.hallway_co
    options:
      threshold:
        type: above
        value:
          number: 20
          unit_of_measurement: "ppm"
      behavior: any
actions:
  - action: notify.send_message
    target:
      entity_id: notify.my_device
    data:
      title: "CO level elevated at home"
      message: >
        The hallway CO reading is above 20 ppm.
        Open the windows before settling in.

Still stuck?

The Home Assistant community is quick to help: join Discord for real-time chat, post on the community forum with the condition you’re using and what you expected to happen, or share on our subreddit /r/homeassistant.

Related conditions

Explore related conditions:

• Carbon monoxide detected: Tests if one or more carbon monoxide sensors are detecting carbon monoxide.

• Carbon monoxide cleared: Tests if one or more carbon monoxide sensors are cleared.