A push notification model usually breaks in one of two ways: a second phone stops receiving anything, or notifications keep arriving for the account that just signed out. Both come from storing one push address per user. Store one row per app installation instead, with the user ID as a field, and someone with a phone and a tablet has two rows that a single query returns.

The sign-out half has an ordering trap. Delete the installation row while the user is still signed in, then call signOut. A security rule that compares the row owner to the signed-in user refuses the delete once there is no user left to compare against, and the device keeps pointing at the previous account.

The full write-up covers the Firestore rules, the Flutter registration listener, a server cleanup that handles both unregistered error codes, and an acceptance sequence to run on two test installations.

Great technical breakdown! Handling multi-device FCM tokens and secure sign-out correctly is essential for reliable push notifications. I appreciate the focus on both architecture and real-world edge cases. 👏

Built Heightly, a web app that measures your height with just your phone camera and a sheet of paper.

Parents still track their kids’ growth with pencil marks on a door frame, and most height apps either need AR (which doesn’t work in iPhone browsers) or just guess. I wanted something anyone can open from a link, on any phone, so I built it on Base44:

📄 A sheet of A4 paper becomes the ruler. The app finds it automatically and snaps to its edges 🧍 Real-time body detection finds the head and feet and guides you into place (paper, distance, straight phone, height) 🎯 Takes 10 readings, locks the result in about 10 seconds, and refuses impossible results instead of guessing 📈 Saves heights for the whole family, calculates growth automatically and flags who’s due to measure again 🔒 Privacy first: photos stay on your phone

Process: I designed every screen first, then built and tested it. My first version showed a random number 😅, so I added pose detection and a paper-based scale, then fixed issues like distance changing the result, until a known-height test read within about 1 cm.

Live App: https://grow-track-spot.base44.app