PM4 level changed

The PM4 level changed trigger fires after the PM4 (particulate matter 4 micrometers or smaller) reading on one or more air quality sensors changes. PM4 particles come from sources like pollen, mold spores, dust, and certain industrial processes. They sit between the finer PM2.5 and the coarser PM10 range, giving you an additional view of the particles floating in your air. If you deal with seasonal allergies or live near a dusty road, tracking PM4 helps you spot irritants before your nose does.

Imagine your home office air purifier starting as soon as pollen counts rise on a spring afternoon, so you stay focused instead of reaching for tissues. Use this trigger to start filtration, log changes, or notify household members when PM4 readings change. Use the threshold type to filter which changes matter to your automation.

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 PM4 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 PM4 sensor is in (like your living room 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 PM4 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 level in μg/m³, 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. 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, 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.pm4_changed. A basic example looks like this:

trigger: air_quality.pm4_changed
target:
  entity_id: sensor.office_pm4
options:
  threshold:
    type: above
    value:
      number: 10

This fires whenever the office PM4 sensor reading changes to a value above 10 μg/m³. To fire on any change, use type: any and leave out value.

Options in YAML

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 PM4 sensor behind that target.

• Entity: one specific PM4 sensor, such as sensor.living_room_pm4.
• Device: every PM4 sensor that belongs to a device.
• Area: every PM4 sensor in a room or area.
• Floor: every PM4 sensor on a floor.
• Label: every PM4 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.

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

• PM4 fills the gap between PM2.5 and PM10 measurements, which is useful if your sensor reports this size range separately.
• The threshold type controls which changes fire the trigger. Use Above or Below to fire only when the new level is above or below a value, In range to fire only when it’s inside a range, and Outside range to fire only when it’s outside a range. Use Any change to fire on every change.
• To react only when PM4 crosses a specific concentration in one direction, use PM4 level crossed threshold instead.
• The threshold is in μg/m³. A sensor that reports PM4 in another unit never matches. If you use an entity as the threshold, it must also report μg/m³.

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: notify when office PM4 shifts

Allergy season and dusty days make it hard to focus when you work from home. This automation sends a notification when PM4 levels in your home office change to a value above 10 μg/m³, so you know exactly when to turn on the air purifier or crack a window.

• Trigger: PM4 level changed
  • Target: Office PM4 sensor
  • Threshold type: Above 10 μg/m³
• Action: Send a notification message
  • Target: My Device (notify.my_device)

alias: "Notify on office PM4 change"
triggers:
  - trigger: air_quality.pm4_changed
    target:
      entity_id: sensor.office_pm4
    options:
      threshold:
        type: above
        value:
          number: 10
actions:
  - action: notify.send_message
    target:
      entity_id: notify.my_device
    data:
      title: "PM4 change detected"
      message: "PM4 levels in the office are above 10 μg/m³. Consider turning on the air purifier."

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

Explore related triggers:

• PM4 level crossed threshold: Triggers when one or more PM4 levels cross a threshold.