As a primary last resort there should be a printed paper backup of the database, but it's a snapshot of ticket sales that at this point would be an hour old, and there's always a rush of last minute writes to the database.

The better organised venues write those changes down with a pen, so it's at least up to date, but modern venues have several entrances to get people through the doors faster, so most people won't have the up to date paper backup.

Our system uses a cross platform app on ordinary smart phones to scan tickets. So if a device goes down, you just need to get your hands on another phone.

There's a limited feature set version of the QR code scanner (scan code, screen flashes red or green) that just runs in a web browser on any device with a half decent camera. All you need is the secret URL for the tonights event — which we also expose via a QR code.