Radon value

The Radon value condition passes when a radon sensor’s reading meets the threshold you define. Radon is a naturally occurring radioactive gas that seeps into buildings from the ground. It is colorless and odorless, so a sensor is the only way to know it is there. Levels tend to be highest in rooms that touch the ground, such as basements and ground-floor bedrooms, and they rise and fall with the weather, the season, and how well a room is ventilated.

Radon is measured in becquerels per cubic meter (Bq/m³) or picocuries per liter (pCi/L). Health authorities around the world publish reference levels, often between 100 and 300 Bq/m³ (about 2.7 to 8 pCi/L), above which they recommend taking action. Check the guidance that applies where you live. This condition lets your automation act on real readings, like running a ventilation fan only if radon is still elevated when the automation runs, or reminding you to air out a room before you spend the night in it. You can set the threshold in either unit, and Home Assistant converts between them automatically.

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 Radon 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 radon sensor is in (like your basement or bedroom). You can also select a device, a specific entity, or a label.
5. From the conditions shown for that target, select Radon 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 radon concentration directly, for example 100 for 100 Bq/m³. 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 radon unit (Bq/m³ or pCi/L) 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. For how an automation is built in YAML, refer to Automations in YAML.

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_radon_value. A basic example looks like this:

condition: air_quality.is_radon_value
target:
  entity_id: sensor.basement_radon
options:
  threshold:
    type: above
    value:
      number: 100
      unit_of_measurement: "Bq/m³"

This passes when the basement radon reading is above 100 Bq/m³.

You can set the threshold in pCi/L even if your sensors report in Bq/m³. Home Assistant converts the values before comparing them. To check that every bedroom sensor is below a limit:

condition: air_quality.is_radon_value
target:
  entity_id:
    - sensor.main_bedroom_radon
    - sensor.guest_bedroom_radon
options:
  threshold:
    type: below
    value:
      number: 4
      unit_of_measurement: "pCi/L"
  behavior: all

This passes when both bedroom readings are below 4 pCi/L (148 Bq/m³).

To use a user-created helperA helper is a virtual entity you create inside Home Assistant. It is not backed by a physical device. Helpers store values, track state, or do calculations that your automations and dashboards need. [Learn more] as a dynamic threshold that you can adjust without editing the automation:

condition: air_quality.is_radon_value
target:
  entity_id: sensor.basement_radon
options:
  threshold:
    type: above
    value:
      entity: input_number.radon_action_level

Set the helper’s unit of measurement to Bq/m³ or pCi/L, because an entity without one of those units never matches.

Options in YAML

threshold:
  type: between
  value_min:
    entity: input_number.radon_lower_limit
  value_max:
    number: 300
    unit_of_measurement: "Bq/m³"

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 radon sensor behind that target.

• Entity: one specific radon sensor, such as sensor.basement_radon.
• Device: every radon sensor that belongs to a device.
• Area: every radon sensor in a room or area.
• Floor: every radon sensor on a floor.
• Label: every radon 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.

To leave out some of these entities, refer to Excluding targets. For example, you can leave out one radon sensor in an area.

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

• This condition works with sensors that have the radon device class.
• Supported radon units are Bq/m³ and pCi/L. The threshold and the sensor can use different units. Home Assistant converts both to Bq/m³ before comparing them, so 4 pCi/L and 148 Bq/m³ are treated as the same level.
• Supported thresholds can use fixed values, a sensor with the radon device class, a number entity with the radon device class, or a user-created helperA helper is a virtual entity you create inside Home Assistant. It is not backed by a physical device. Helpers store values, track state, or do calculations that your automations and dashboards need. [Learn more] from the Input number integration. When you use an entity, its current value is read each time the condition runs.
• Entities that are unavailable or unknown are skipped when the condition is evaluated. With Any, at least one remaining valid sensor must match. With All, every remaining valid sensor must match.
• Radon is an indoor air quality concern, so it often pairs well with Carbon dioxide value and Volatile organic compounds value when deciding whether a room needs ventilation.

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: run the basement fan overnight only if radon is high

Radon often builds up in a closed basement during the day. This automation runs at 22:00 and checks the basement radon reading. If the level is above 100 Bq/m³, the ventilation fan turns on so the air is cleared before morning. On days when the reading has stayed low, nothing happens. This automation only turns the fan on, so use a separate automation or schedule to turn it off.

• Trigger: Time: 22:00
• Condition: Radon value (above 100 Bq/m³)
  • Target: Basement radon sensor
• Action: Turn on fan
  • Target: Basement ventilation fan

alias: "Ventilate basement overnight when radon is high"
triggers:
  - trigger: time
    at: "22:00:00"
conditions:
  - condition: air_quality.is_radon_value
    target:
      entity_id: sensor.basement_radon
    options:
      threshold:
        type: above
        value:
          number: 100
          unit_of_measurement: "Bq/m³"
actions:
  - action: fan.turn_on
    target:
      entity_id: fan.basement_ventilation

Automation: remind you to air out the bedroom when you get home

If a bedroom sensor shows elevated radon, you want to know before you sleep there, not after. This automation triggers when you enter the home zone and checks the bedroom radon reading. If the level is above 4 pCi/L, you get a notification suggesting you open the windows for a while. The threshold is set in pCi/L, and Home Assistant converts it automatically if the sensor reports in Bq/m³.

• Trigger: Zone entered
  • Target: Frenck
  • Zone: Home
• Condition: Radon value (above 4 pCi/L)
  • Target: Bedroom radon sensor
• Action: Send a notification message
  • Target: My Device (notify.my_device)

alias: "Radon reminder on arrival home"
triggers:
  - trigger: zone.entered
    target:
      entity_id: person.frenck
    options:
      zone: zone.home
conditions:
  - condition: air_quality.is_radon_value
    target:
      entity_id: sensor.bedroom_radon
    options:
      threshold:
        type: above
        value:
          number: 4
          unit_of_measurement: "pCi/L"
actions:
  - action: notify.send_message
    target:
      entity_id: notify.my_device
    data:
      title: "Radon is elevated in the bedroom"
      message: >
        The bedroom radon reading is above 4 pCi/L.
        Open the windows for a while before bedtime.

Still stuck?

To find out why the condition didn’t pass, check it live in the automation editor, and look at the trace of the run. 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 condition you’re using and what you expected to happen, or share on our subreddit /r/homeassistant.

Related conditions

Explore related conditions:

• Carbon dioxide value: Tests the carbon dioxide level of one or more entities.

• Volatile organic compounds value: Tests the volatile organic compounds level of one or more entities.