Class change alerts for a gym or studio

What this actually looks like

A cancelled class nobody hears about is fifteen people at a locked door. A channel members subscribe to once carries the change the moment you know it, and carries next week’s timetable as a picture when the whole thing shifts.

How you would set it up

1. Create a channel for the studio and put its QR code at reception and in the changing rooms.
2. Send changes immediately, and schedule the weekly timetable the night before.
3. Attach the new timetable as an image so nobody has to open a website to read it.

Draft, schedule, send — and what cancelling cannot undo

Composing and sending are deliberately different permissions, so the person or script that writes an alert can be forbidden from publishing it. A scheduled alert becomes visible at its time without anything having to run at that minute, which means a server that was briefly down delivers late rather than never. Cancelling is honest about its limits: it stops an alert reaching phones that have not fetched it yet and does nothing at all to the phones that already have it. An alert cannot be unsent.

One handle, printed once, permanent

A channel lives at drop.top followed by its handle, and that address never changes. It cannot be edited after creation, because it ends up on a poster in a school entrance, on a festival gate and inside a QR code somebody has already laminated. The page behind it explains what the channel is, what it asks a phone for, and how to subscribe — so a stranger reading a poster can decide before installing anything. We generate the QR code for you, server-side, and it is never sent to a third-party image service.

A picture, a sound or a document, when words are not enough

A diverted bus route is a map. A boil-water notice is a paragraph of instructions people will re-read. An alert can carry an image, a sound file or a document alongside the text. Documents are stored exactly as written and re-rendered from a sanitised copy rather than being run as markup, so an attachment cannot turn into a script on somebody’s lock screen. The bytes are uploaded once and attached by reference, which keeps a send cheap however large the audience.