What we learned shipping offline scanning

Doors are the one place a ticketing platform cannot afford to be slow. A scanner that hesitates for two seconds per guest turns a thousand-person event into a thirty-minute queue. So when we rebuilt the scanner app this quarter, the brief was narrow: scan fast, work offline, never double-admit.

The hard requirement is that the venue's network is assumed to be bad. The scanner downloads the full door list when it has signal, pins it locally, and from then on every scan is a local lookup — green or red in under a beat, no round-trip.

Reconciliation is where it gets interesting. Two scanners at two gates can scan the same ticket within seconds of each other while both are offline. We resolve it server-side: first scan by timestamp wins, the second surfaces as a duplicate in the dashboard. The door staff see red instantly; the back office sees why later.

None of this is glamorous, and that's the point. The best thing a scanner can do is disappear — a quiet beep, a green light, and the queue keeps moving.