Expose to KNX bus

The Expose to KNX bus action adds or removes an exposure that sends a Home Assistant entity state or attribute to a KNX group address. Once registered, state and attribute updates are written to the bus, and GroupValueRead requests for that address are answered.

This is useful when you want other KNX devices to react to or read Home Assistant values, and to manage those exposures dynamically instead of defining them all up front.

Exposures defined through your configuration.yamlThe configuration.yaml file is the main configuration file for Home Assistant. It lists the integrations to be loaded and their specific configurations. In some cases, the configuration needs to be edited manually directly in the configuration.yaml file. Most integrations can be configured in the UI. [Learn more] cannot be removed with this action. Per address, only one exposure can be registered. For more details, and for additional exposure options like value_template, cooldown, periodic_send, and respond_to_read, see the Exposing entity states, entity attributes or time to KNX bus section.

Using this action from the user interface

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

To register an exposure from an automation or a script:

1. Go to Settings > Automations & scenes.
2. Open an existing automation or script, or select Create automation > Create new automation.
3. If you’re setting up a new automation, add a trigger in the When section. Scripts don’t need a trigger. They run when something else calls them.
4. In the Then do section, select Add action.
5. From the search box, search for and select KNX: Expose to KNX bus.
6. Enter the Group address, the Value type, and the Entity to expose. Optionally, set an Entity attribute and a Default value, or turn on Remove exposure to remove the exposure.
7. Select Save.

This action does not support targets. In the UI, you are not prompted to choose an area, device, entity, or label. Only users with administrator rights can run this action.

Options in the UI

Using this action 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 action as knx.exposure_register. A basic example looks like this:

action: knx.exposure_register
data:
  address: "1/1/0"
  type: percentU8
  entity_id: light.living_room
  attribute: brightness
  default: 0

This exposes the brightness of light.living_room to group address 1/1/0.

Options in YAML

Try it yourself

Ready to test this? Open Developer tools > Actions, search for this action, fill in the fields, and select Perform action. You see what happens 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] without writing a line of YAML.

Still stuck?

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

Related actions

These actions work well alongside this one:

• Send to KNX bus: Sends arbitrary data directly to the KNX bus.

• Read from KNX bus: Sends GroupValueRead requests to the KNX bus.

• Register knx_event: Adds or removes group addresses in the knx_event filter.