What is mobile-apps-fcm-push?

Home Assistant's mobile apps can send push notifications to your phone, like an alert when your front door opens or the laundry is done. This repository contains the backend code that actually delivers those notifications. It acts as the middleman between your Home Assistant server and Apple's and Google's push notification services, making sure alerts reach your device quickly and reliably. At a high level, the code runs on Firebase, a Google-backed platform for hosting small server-side functions. When your Home Assistant instance wants to send a notification, it triggers one of these functions. The function then formats the message and hands it off to the appropriate mobile platform, Firebase Cloud Messaging for Android or Apple Push Notification service for iOS, which routes it to your phone. The project is written in JavaScript and uses NPM for managing dependencies. The main audience here isn't everyday Home Assistant users, the official mobile apps already use this code behind the scenes. Instead, it's for developers who want to contribute to the project, perhaps to fix a bug or add a feature, or for people who want to run their own notification backend instead of relying on the official one. For example, someone self-hosting everything might prefer to deploy their own instance in a European data center rather than the default US-based one, and the setup instructions support that. The README is fairly sparse and mostly focuses on developer setup and deployment steps. It doesn't go into much detail on the internal architecture or how specific edge cases are handled. What's notable is that this is a small, focused piece of infrastructure: it does one job, relaying notifications, and is designed to run as serverless functions rather than a traditional always-on server.