> ## Documentation Index > Fetch the complete documentation index at: https://mintlify.com/home-assistant/core/llms.txt > Use this file to discover all available pages before exploring further. # Event Helpers > Helper functions for listening to and tracking events in Home Assistant. The `homeassistant.helpers.event` module provides utilities for listening to events, tracking state changes, and managing time-based operations. ## Key Functions ### async\_track\_state\_change\_event Track specific state change events indexed by entity\_id. Home Assistant instance Entity IDs to track (automatically lowercased) Callback function to execute when state changes Job type for the callback Function to call to remove the listener ```python theme={null} from homeassistant.helpers.event import async_track_state_change_event def my_callback(event): print(f"State changed: {event.data['entity_id']}") remove_listener = async_track_state_change_event( hass, ["light.living_room", "light.bedroom"], my_callback ) ``` ### async\_track\_state\_report\_event Track EVENT\_STATE\_REPORTED by entity\_ids. This fires when state is updated but not changed. Home Assistant instance Entity IDs to track Callback function to execute Job type for the callback ### async\_track\_point\_in\_time Add a listener that fires once at or after a specific point in time. Home Assistant instance Callback to execute (passed the time it fires in local time) Point in time to fire the callback ### async\_track\_template\_result Add a listener that fires when the result of a template changes. Home Assistant instance List of templates to track Callback to call with results When True, raise on undefined variables Optional custom logging function for template errors When True, first template blocks rendering of others if it doesn't render as True Object used to unregister the listener and refresh the template ## Data Classes ### TrackStates Class for keeping track of states being tracked. Whether all states on the system are being tracked Lowercased entities to track Lowercased domains to track ### TrackTemplate Class for keeping track of a template with variables. Template to calculate Variables to pass to the template Rate limit on how often the template is re-rendered ### TrackTemplateResult Class for result of template tracking. The template that has changed Output from the template on the last successful run (None if no previous run) Result from the template run (string or TemplateError if template errored) ## Device and Entity Registry Tracking ### async\_track\_entity\_registry\_updated\_event Track specific entity registry updated events indexed by entity\_id. Home Assistant instance Entity IDs to track (must be lowercase) Callback function Job type for the callback ### async\_track\_device\_registry\_updated\_event Track specific device registry updated events indexed by device\_id. Home Assistant instance Device IDs to track Callback function Job type for the callback ## Constants * `RANDOM_MICROSECOND_MIN = 50000` - Minimum microseconds for spreading listeners * `RANDOM_MICROSECOND_MAX = 500000` - Maximum microseconds for spreading listeners * `EVENT_STATE_CHANGED` - Event type for state changes * `EVENT_STATE_REPORTED` - Event type for state reports (update without change)