Radon level changed

The Radon level changed trigger fires after the radon reading on one or more air quality sensors changes. Radon is a naturally occurring radioactive gas that rises from the soil and seeps into buildings through cracks and gaps in floors and walls, so it tends to collect in basements, crawl spaces, and ground-floor rooms. You cannot see or smell it, and long-term exposure to elevated levels increases the risk of lung cancer. Indoor radon levels also drift up and down over the day with ventilation, weather, and soil conditions, so a live sensor tells you far more than a one-time test.

Use the threshold type to decide which changes matter. Fire on any change to track trends, or only when the new reading lands above or below a level you choose. Imagine your basement ventilation fan switching on by itself as soon as a reading comes in above your limit, or a notification with the latest value while levels stay elevated. Radon sensors report in becquerels per cubic meter (Bq/m³) or picocuries per liter (pCi/L). You can set the threshold in either unit, and Home Assistant converts between them automatically.

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 Radon level changed 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 radon sensor is in (like your basement or bedroom). You can also select a device, a specific entity, or a label. When you target multiple entities (via area, label, or multiple entity selections), the trigger fires whenever any of them changes.
5. From the triggers shown for that target, select Radon level changed.
6. Under Threshold type, configure what kind of change fires the trigger:
   • Select Any change to fire on any change, regardless of direction or new value.
   • Select Above or Below and enter a value to fire only when the new reading is above or below that value.
   • Select In range and enter a lower and upper bound to fire only when the new reading falls inside the range.
   • Select Outside range and enter a lower and upper bound to fire only when the new reading is outside the range.
   • For each option, you can enter a fixed radon concentration, pick a sensor entity or a number helper entity as the threshold.
     • 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. 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.radon_changed. A basic example looks like this:

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

This fires whenever the basement radon sensor reading changes to a value above 100 Bq/m³. If the sensor reports in pCi/L, Home Assistant converts the reading before comparing it.

To fire on every change, regardless of direction or the new value, use type: any and omit value:

trigger: air_quality.radon_changed
target:
  entity_id: sensor.basement_radon
options:
  threshold:
    type: any

Options in YAML

threshold:
  type: outside
  value_min:
    entity: input_number.radon_reference_level
  value_max:
    number: 300
    unit_of_measurement: "Bq/m³"

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 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 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.

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

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.

Good to know

• Use a sensor with the radon device class as the target.
• If you use an entity as the threshold, it must report its unit of measurement as Bq/m³ or pCi/L. A user-created number 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] without one of those units cannot be used as a threshold, and the trigger does not fire.
• Radon sensors report in Bq/m³ or pCi/L. You can set the threshold in either unit, and Home Assistant converts the sensor reading and the threshold to the same unit before comparing them, so a sensor that reports in pCi/L works with a threshold set in Bq/m³ and the other way around. 1 pCi/L equals 37 Bq/m³.
• The threshold type controls both the direction and the landing zone of the change. Use Above or Below to filter by direction, In range to fire only when the new value is inside a range, and Outside range to fire only when it escapes a range.
• Use Any change to fire on every change regardless of direction or where the new value lands.
• 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.
• Guidance on indoor radon varies by country. Reference levels between 100 Bq/m³ and 300 Bq/m³ are commonly cited, and 4 pCi/L (about 150 Bq/m³) is a widely used action level. Radon fluctuates from hour to hour and season to season, so look at long-term averages before deciding on remediation, and check the guidance that applies where you live.
• To react only when radon first crosses a specific level, use Radon 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, 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: keep the basement ventilated while radon stays high

Radon collects in the lowest, least ventilated parts of a home. This automation turns on the basement ventilation fan every time a new reading above 100 Bq/m³ comes in, so the fan stays on for as long as the level is elevated, even if someone switched it off by hand.

• Trigger: Radon level changed
  • Target: Basement radon sensor
  • Threshold type: Above (100 Bq/m³)
• Action: Turn on fan

alias: "Ventilate basement while radon is high"
triggers:
  - trigger: air_quality.radon_changed
    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: get the latest reading while any room is above 4 pCi/L

If you have radon sensors in several rooms, this automation keeps you posted with the current reading from whichever sensor reports a value above 4 pCi/L. The threshold is set in pCi/L, and Home Assistant converts readings from sensors that report in Bq/m³ automatically.

• Trigger: Radon level changed
  • Target: All radon sensors (by label)
  • Threshold type: Above (4 pCi/L)
• Action: Send a notification message
  • Target: My Device (notify.my_device)

alias: "Notify on elevated radon reading"
triggers:
  - trigger: air_quality.radon_changed
    target:
      label_id: radon_sensors
    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: "Elevated radon level"
      message: >
        {{ trigger.to_state.name }} reports
        {{ trigger.to_state.state }}
        {{ trigger.to_state.attributes.unit_of_measurement }}.
        Consider airing out the room.

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:

• Radon level crossed threshold: Triggers when one or more radon levels cross a threshold.