Proof of concept for implementing triggers in a different domain

homeassistant/components/binary_sensor/icons.json

@@ -176,6 +176,9 @@
     }
   },
   "triggers": {
+    "door.opened": {
+      "trigger": "mdi:door-open"
+    },
     "occupancy_cleared": {
       "trigger": "mdi:home-outline"
     },

homeassistant/components/binary_sensor/strings.json

@@ -332,6 +332,16 @@
   },
   "title": "Binary sensor",
   "triggers": {
+    "door.opened": {
+      "description": "Triggers after one or more occupancy doors open.",
+      "fields": {
+        "behavior": {
+          "description": "[%key:component::binary_sensor::common::trigger_behavior_description_occupancy%]",
+          "name": "[%key:component::binary_sensor::common::trigger_behavior_name%]"
+        }
+      },
+      "name": "Door opened"
+    },
     "occupancy_cleared": {
       "description": "Triggers after one or more occupancy sensors stop detecting occupancy.",
       "fields": {

homeassistant/components/binary_sensor/trigger.py

@@ -53,6 +53,7 @@ def make_binary_sensor_trigger(
 
 
 TRIGGERS: dict[str, type[Trigger]] = {
+    "_door.opened": make_binary_sensor_trigger(BinarySensorDeviceClass.DOOR, STATE_ON),
     "occupancy_detected": make_binary_sensor_trigger(
         BinarySensorDeviceClass.OCCUPANCY, STATE_ON
     ),

homeassistant/components/binary_sensor/triggers.yaml

@@ -23,3 +23,10 @@ occupancy_detected:
     entity:
       domain: binary_sensor
       device_class: occupancy
+
+_door.opened:
+  fields: *trigger_common_fields
+  target:
+    entity:
+      domain: binary_sensor
+      device_class: door

homeassistant/helpers/trigger.py

@@ -121,7 +121,7 @@ def starts_with_dot(key: str) -> str:
 _TRIGGERS_DESCRIPTION_SCHEMA = vol.Schema(
     {
         vol.Remove(vol.All(str, starts_with_dot)): object,
-        cv.underscore_slug: vol.Any(None, _TRIGGER_DESCRIPTION_SCHEMA),
+        str: vol.Any(None, _TRIGGER_DESCRIPTION_SCHEMA),
     }
 )
 
@@ -1433,6 +1433,10 @@ async def async_get_all_descriptions(
         if (target := yaml_description.get("target")) is not None:
             description["target"] = target
 
+        prefix, sep, _ = missing_trigger.partition(".")
+        if sep and domain != prefix:
+            description["translation_domain"] = domain
+
         new_descriptions_cache[missing_trigger] = description
     hass.data[TRIGGER_DESCRIPTION_CACHE] = new_descriptions_cache
     return new_descriptions_cache