Nitrogen monoxide level changed

The Nitrogen monoxide level changed trigger fires after the nitrogen monoxide (NO) reading on one or more air quality sensors changes by a meaningful amount. Nitrogen monoxide is a reactive gas produced mainly by vehicle engines and combustion processes. It quickly converts to nitrogen dioxide in the atmosphere and plays a key role in smog formation. If you live near a busy road or intersection, rush-hour traffic sends NO levels climbing, and that pollution easily seeps indoors through open windows.

Imagine your home automatically logging pollution patterns near the driveway so you know which hours to keep the windows shut. Use this trigger to track pollution data, activate ventilation, or send alerts whenever your NO 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 Nitrogen 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.no_changed. A basic example looks like this:

trigger: air_quality.no_changed
target:
  entity_id: sensor.driveway_no
options:
  threshold: 10

This fires whenever the driveway NO sensor reading changes by at least 10 ppb.

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

• Nitrogen monoxide levels spike near busy roads and during rush hour. Monitoring helps you time ventilation to avoid peak traffic pollution.
• The trigger fires on any change that meets the threshold, whether the level goes up or down.
• To react only when NO crosses a specific concentration in one direction, use Nitrogen 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: log roadside pollution changes

Rush-hour traffic sends NO levels spiking near the road, and knowing the pattern helps you decide when to open or close the windows. This automation records a log entry whenever nitrogen monoxide levels near the driveway shift, helping you spot pollution trends over time.

• Trigger: Nitrogen monoxide level changed
• Target: Driveway NO sensor
• Threshold type: 10
• Action: Log entry via logbook

alias: "Log NO level changes"
triggers:
  - trigger: air_quality.no_changed
    target:
      entity_id: sensor.driveway_no
    options:
      threshold: 10
actions:
  - action: logbook.log
    data:
      name: "Air quality"
      message: "Nitrogen monoxide level near the driveway changed."

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:

• Nitrogen monoxide level crossed threshold - Triggers after one or more nitrogen monoxide levels cross a threshold.