Home Assistant notifications on the TV

Home Assistant already knows how to send Telegram messages through the telegram_bot integration. Point a notify service at a "Home" group, enable the overlay on that group in Tevegram, and every automation that calls notify shows up over the TV picture. Nothing to install on the Home Assistant side beyond the Telegram integration.

Does it work on my TV?

What you need

Home Assistant with the Telegram bot integration (Settings, Devices & services, Add integration, "Telegram bot"; YAML also works, see below).
A Telegram bot token from @BotFather (/newbot), the bot added to a dedicated "Home" group, and that group's chat id (send a message in the group and forward it to @getidsbot, or read the "chat":{"id"} field from https://api.telegram.org/bot<TOKEN>/getUpdates; group ids start with -100).
An Android TV or Google TV with Tevegram signed in to the account that is a member of the "Home" group.

Setup

Configure the Telegram bot and a notify service in Home Assistant. Either add the "Telegram bot" integration from the UI (polling mode, paste the token, allow the group's chat id), or declare it in configuration.yaml as in the excerpt below. Restart Home Assistant.
Call notify.tv from an automation. In any automation, add the action "Notifications: Send a notification via tv" with your message. The excerpt shows the YAML form. Keep messages short: they are read on a TV from the couch.
Enable the overlay on the "Home" group in Tevegram. On the TV, in the Chats tab, select the "Home" group and turn on its notification bell. Allow "Display over other apps" when Android asks. From now on, every message posted in that group appears over the TV picture.
Test. Trigger the automation, or type a message in the group from your phone. It should appear on the TV within a second or two, then fade out.

Configuration

configuration.yaml, plus the action of an automation

telegram_bot:
  - platform: polling
    api_key: !secret telegram_bot_token
    allowed_chat_ids:
      - -1001234567890   # chat id of the "Home" group

notify:
  - platform: telegram
    name: tv
    chat_id: -1001234567890

# In an automation:
action:
  - service: notify.tv
    data:
      message: "Doorbell: someone is at the door"

Good to know

Photos from cameras

notify.tv can also send a camera snapshot (data: photo: url or file). The photo lands in the group and is visible in Tevegram; the overlay itself shows the text, so put the useful information in the message.

One group, one bell

Sending everything to a single "Home" group keeps the Tevegram side to one toggle. If you want alerts on the TV but chatter elsewhere, use two groups and enable the bell on the alerts one only.

Frequently asked questions

Does the TV need to be on Tevegram?

No. Tevegram runs in the background and draws the overlay over whatever is on screen: live TV, another app, the home screen. Open it once after the TV has been turned on if notifications stop appearing.

Will my other chats interrupt the TV too?

Only if you turn their bell on. Keep the overlay enabled on the "Home" group alone and the TV shows nothing else.

Can I send to the TV only when it is on?

Telegram does not know about the TV, but Home Assistant does: add a condition on your TV's media_player state (or its power plug) to the automation, so alerts are only sent when someone is watching.