TY.
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Case study 04/Private messaging app/2026

Mine.

A closed, invite-only app for exactly two paired people to exchange taps and short notes in real time — Firestore snapshots for delivery, a Node push relay for notifications, and restrictive security rules so each person reaches only their own and their partner’s data. Biometric lock, haptics, and a keep-alive cron for the free-tier relay.

Role
Design & app build
Stack
Expo · Firebase · Node
Users
Two — in daily use
Status
Rebuild in progress

( Overview )

The whole point of Mine is how little it does. Two paired people, one private channel — no feed, no followers, no third account — just taps and short notes passing between them in real time.

Delivery rides on Firestore snapshots; notifications go through a small Node push relay, kept awake on the free tier by a keep-alive cron. Restrictive security rules mean each person can reach only their own and their partner’s data, and the app itself sits behind a biometric lock.

01

Paired, and nothing else

Invite-only for exactly two people, with restrictive rules scoping each person to their own and their partner’s data.

02

Real-time by snapshot

Taps and short notes arrive live over Firestore snapshots, with haptics on the device.

03

Notifications on a budget

A Node push relay delivers alerts; a keep-alive cron holds the free-tier relay awake.

Have a private tool in mind?