Road closure alerts
Setting this up takes about a minute. The slow part is not the software — it is deciding what to call yourself, because the handle ends up on a poster and cannot be changed afterwards.
Draw a circle without knowing who is inside it
You place a centre and a radius on a map, and the circle travels attached to the alert. Every subscriber’s phone receives it and compares its own position locally, then decides whether to show it. No subscriber position is ever sent to us, which is why this is a design fact rather than a promise: there is no column anywhere that could hold one. Two consequences follow deliberately. A geofence only ever narrows — it cannot add somebody who did not subscribe. And it fails open: a phone that cannot work out where it is shows the alert rather than hiding it, because missing an evacuation is worse than seeing one meant for the next street.
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.
Questions, answered plainly
Do you know where my subscribers are?
No. The circle is sent with the alert and each phone compares its own position locally. We hold no subscriber location, so there is nothing to leak, subpoena or lose. A phone that cannot determine its position shows the alert rather than hiding it.
Can I attach a map or a PDF?
You can attach an image, a sound file or a document. A document is stored exactly as submitted and rendered from a sanitised copy, so it can never execute anything on a subscriber’s phone.
Do subscribers need an account?
No. They install the app, subscribe to a handle, and that is the whole of it. Only the person running the channel signs up for anything.
How do people find my channel?
From the handle you give them: on a poster, in an enrolment email, on a QR code, in a footer. Public channels also appear in the app’s discover list. Sealed ones appear nowhere at all, by design.
Say it once. Every subscribed phone gets it.
Free up to 100 subscribers, no card to start, and the handle is yours permanently.
Start a channel