diff --git a/homeassistant/helpers/device_registry.py b/homeassistant/helpers/device_registry.py
index 2ff444da89f..4818de83cb9 100644
--- a/homeassistant/helpers/device_registry.py
+++ b/homeassistant/helpers/device_registry.py
@@ -2,7 +2,7 @@
 from asyncio import Event
 from collections import OrderedDict
 import logging
-from typing import List, Optional, cast
+from typing import Any, Dict, List, Optional, cast
 import uuid
 
 import attr
@@ -48,7 +48,7 @@ class DeviceEntry:
     is_new = attr.ib(type=bool, default=False)
 
 
-def format_mac(mac):
+def format_mac(mac: str) -> str:
     """Format the mac address string for entry into dev reg."""
     to_test = mac
 
@@ -260,7 +260,7 @@ class DeviceRegistry:
 
         return new
 
-    def async_remove_device(self, device_id):
+    def async_remove_device(self, device_id: str) -> None:
         """Remove a device from the device registry."""
         del self.devices[device_id]
         self.hass.bus.async_fire(
@@ -298,12 +298,12 @@ class DeviceRegistry:
         self.devices = devices
 
     @callback
-    def async_schedule_save(self):
+    def async_schedule_save(self) -> None:
         """Schedule saving the device registry."""
         self._store.async_delay_save(self._data_to_save, SAVE_DELAY)
 
     @callback
-    def _data_to_save(self):
+    def _data_to_save(self) -> Dict[str, List[Dict[str, Any]]]:
         """Return data of device registry to store in a file."""
         data = {}
 
@@ -327,7 +327,7 @@ class DeviceRegistry:
         return data
 
     @callback
-    def async_clear_config_entry(self, config_entry_id):
+    def async_clear_config_entry(self, config_entry_id: str) -> None:
         """Clear config entry from registry entries."""
         remove = []
         for dev_id, device in self.devices.items():
diff --git a/homeassistant/helpers/discovery.py b/homeassistant/helpers/discovery.py
index 8e4def77440..a6162dbde55 100644
--- a/homeassistant/helpers/discovery.py
+++ b/homeassistant/helpers/discovery.py
@@ -5,6 +5,8 @@ There are two different types of discoveries that can be fired/listened for.
  - listen_platform/discover_platform is for platforms. These are used by
    components to allow discovery of their platforms.
 """
+from typing import Callable, Collection, Union
+
 from homeassistant import core, setup
 from homeassistant.const import ATTR_DISCOVERED, ATTR_SERVICE, EVENT_PLATFORM_DISCOVERED
 from homeassistant.exceptions import HomeAssistantError
@@ -18,7 +20,9 @@ ATTR_PLATFORM = "platform"
 
 
 @bind_hass
-def listen(hass, service, callback):
+def listen(
+    hass: core.HomeAssistant, service: Union[str, Collection[str]], callback: Callable
+) -> None:
     """Set up listener for discovery of specific service.
 
     Service can be a string or a list/tuple.
@@ -28,7 +32,9 @@ def listen(hass, service, callback):
 
 @core.callback
 @bind_hass
-def async_listen(hass, service, callback):
+def async_listen(
+    hass: core.HomeAssistant, service: Union[str, Collection[str]], callback: Callable
+) -> None:
     """Set up listener for discovery of specific service.
 
     Service can be a string or a list/tuple.
@@ -39,7 +45,7 @@ def async_listen(hass, service, callback):
         service = tuple(service)
 
     @core.callback
-    def discovery_event_listener(event):
+    def discovery_event_listener(event: core.Event) -> None:
         """Listen for discovery events."""
         if ATTR_SERVICE in event.data and event.data[ATTR_SERVICE] in service:
             hass.async_add_job(
@@ -73,7 +79,9 @@ async def async_discover(hass, service, discovered, component, hass_config):
 
 
 @bind_hass
-def listen_platform(hass, component, callback):
+def listen_platform(
+    hass: core.HomeAssistant, component: str, callback: Callable
+) -> None:
     """Register a platform loader listener."""
     run_callback_threadsafe(
         hass.loop, async_listen_platform, hass, component, callback
@@ -81,7 +89,9 @@ def listen_platform(hass, component, callback):
 
 
 @bind_hass
-def async_listen_platform(hass, component, callback):
+def async_listen_platform(
+    hass: core.HomeAssistant, component: str, callback: Callable
+) -> None:
     """Register a platform loader listener.
 
     This method must be run in the event loop.
@@ -89,7 +99,7 @@ def async_listen_platform(hass, component, callback):
     service = EVENT_LOAD_PLATFORM.format(component)
 
     @core.callback
-    def discovery_platform_listener(event):
+    def discovery_platform_listener(event: core.Event) -> None:
         """Listen for platform discovery events."""
         if event.data.get(ATTR_SERVICE) != service:
             return
diff --git a/homeassistant/helpers/entity_component.py b/homeassistant/helpers/entity_component.py
index becd96bf5f3..84aa8becafd 100644
--- a/homeassistant/helpers/entity_component.py
+++ b/homeassistant/helpers/entity_component.py
@@ -5,13 +5,14 @@ from itertools import chain
 import logging
 
 from homeassistant import config as conf_util
+from homeassistant.config_entries import ConfigEntry
 from homeassistant.const import (
     ATTR_ENTITY_ID,
     CONF_ENTITY_NAMESPACE,
     CONF_SCAN_INTERVAL,
     ENTITY_MATCH_ALL,
 )
-from homeassistant.core import callback
+from homeassistant.core import HomeAssistant, callback
 from homeassistant.exceptions import HomeAssistantError
 from homeassistant.helpers import config_per_platform, discovery
 from homeassistant.helpers.config_validation import make_entity_service_schema
@@ -29,7 +30,7 @@ DATA_INSTANCES = "entity_components"
 
 
 @bind_hass
-async def async_update_entity(hass, entity_id):
+async def async_update_entity(hass: HomeAssistant, entity_id: str) -> None:
     """Trigger an update for an entity."""
     domain = entity_id.split(".", 1)[0]
     entity_comp = hass.data.get(DATA_INSTANCES, {}).get(domain)
@@ -158,7 +159,7 @@ class EntityComponent:
 
         return await self._platforms[key].async_setup_entry(config_entry)
 
-    async def async_unload_entry(self, config_entry):
+    async def async_unload_entry(self, config_entry: ConfigEntry) -> bool:
         """Unload a config entry."""
         key = config_entry.entry_id
 
@@ -237,7 +238,7 @@ class EntityComponent:
         await self._platforms[key].async_setup(platform_config, discovery_info)
 
     @callback
-    def _async_update_group(self):
+    def _async_update_group(self) -> None:
         """Set up and/or update component group.
 
         This method must be run in the event loop.
@@ -265,7 +266,7 @@ class EntityComponent:
             )
         )
 
-    async def _async_reset(self):
+    async def _async_reset(self) -> None:
         """Remove entities and reset the entity component to initial values.
 
         This method must be run in the event loop.
@@ -283,7 +284,7 @@ class EntityComponent:
                 "group", "remove", dict(object_id=slugify(self.group_name))
             )
 
-    async def async_remove_entity(self, entity_id):
+    async def async_remove_entity(self, entity_id: str) -> None:
         """Remove an entity managed by one of the platforms."""
         for platform in self._platforms.values():
             if entity_id in platform.entities:
diff --git a/homeassistant/helpers/entity_platform.py b/homeassistant/helpers/entity_platform.py
index 133d1a5841f..e171a4cade8 100644
--- a/homeassistant/helpers/entity_platform.py
+++ b/homeassistant/helpers/entity_platform.py
@@ -1,6 +1,7 @@
 """Class to manage the entities for a single platform."""
 import asyncio
 from contextvars import ContextVar
+from datetime import datetime
 from typing import Optional
 
 from homeassistant.const import DEVICE_DEFAULT_NAME
@@ -64,14 +65,14 @@ class EntityPlatform:
         # which powers entity_component.add_entities
         if platform is None:
             self.parallel_updates = None
-            self.parallel_updates_semaphore = None
+            self.parallel_updates_semaphore: Optional[asyncio.Semaphore] = None
             return
 
         self.parallel_updates = getattr(platform, "PARALLEL_UPDATES", None)
         # semaphore will be created on demand
         self.parallel_updates_semaphore = None
 
-    def _get_parallel_updates_semaphore(self):
+    def _get_parallel_updates_semaphore(self) -> asyncio.Semaphore:
         """Get or create a semaphore for parallel updates."""
         if self.parallel_updates_semaphore is None:
             self.parallel_updates_semaphore = asyncio.Semaphore(
@@ -406,7 +407,7 @@ class EntityPlatform:
 
         await entity.async_update_ha_state()
 
-    async def async_reset(self):
+    async def async_reset(self) -> None:
         """Remove all entities and reset data.
 
         This method must be run in the event loop.
@@ -426,7 +427,7 @@ class EntityPlatform:
             self._async_unsub_polling()
             self._async_unsub_polling = None
 
-    async def async_remove_entity(self, entity_id):
+    async def async_remove_entity(self, entity_id: str) -> None:
         """Remove entity id from platform."""
         await self.entities[entity_id].async_remove()
 
@@ -437,7 +438,7 @@ class EntityPlatform:
             self._async_unsub_polling()
             self._async_unsub_polling = None
 
-    async def _update_entity_states(self, now):
+    async def _update_entity_states(self, now: datetime) -> None:
         """Update the states of all the polling entities.
 
         To protect from flooding the executor, we will update async entities