Doorlist

At a glance

participants at a one-day conference

500

volunteers using the same app

200

the room's size, served comfortably in load tests

8×

findings from a security audit, closed in code

14 of 15

The problem

Checking in hundreds of young people at a single door means long queues and a crowd of volunteers doing nothing but reading names off a list. Once inside, attendees still had to collect the t-shirts, meals and drinks they had paid for in advance, and the organisers needed to know who had already collected what.

The tools the organisers already used covered parts of this, but each separately, and none of them took the queue away.

The solution

Doorlist moves check-in onto the attendee's own phone. Before the event, every participant and volunteer receives a personal ticket code by WhatsApp. On the day, they enter it, confirm the last four digits of their phone number and scan the poster at the venue. The app then gives them a digital pass with their arrival number.

The same app serves everyone else in the room. Volunteers scan passes to hand over the items each attendee is entitled to, and run a live prize draw from the people who have checked in. Organisers get a door lookup for anyone who needs help, a roster they can edit as people arrive, and a live dashboard of the event.

Key features

• Self check-in from any phone

  Three ways in — a typed code, a personal link or the venue poster — all leading to the same resumable flow. Progress survives a reload, and a completed check-in follows the attendee to a new device.

  Why it matters: no queue at the door, and far fewer volunteers needed to staff it.

• A pass that gives away its own screenshot

  Every 30 seconds, the attendee's pass and the volunteer's screen show the same colour and word, derived independently from a shared secret. Neither side asks the other what to show.

  Why it matters: a pass forwarded to a friend is visibly out of date, without the volunteer looking anything up.

• A collection counter that cannot rewrite history

  Volunteers scan a pass, see what the attendee is entitled to and has already collected, and slide to confirm. Every outcome is recorded, and corrections are added as new records rather than edits.

  Why it matters: no t-shirt is claimed twice, and every handover can be traced afterwards.

• Built for a room on one network

  The limits that stop code guessing are keyed on the attendee rather than the network address, the server turns away excess load instead of slowing down, and a repeated tap is answered without doing the work twice.

  Why it matters: hundreds of phones on the venue Wi-Fi share one address, and a tired attendee taps again when a screen is slow.

• One app instead of several

  Ticket delivery, check-in, passes, item collection, the prize draw, a venue map and an anonymous feedback questionnaire all live in the same app, reached from the attendee's pass.

  Why it matters: attendees and volunteers learn one tool, and the organisers see the whole event in one place.

Under the hood

For technical readers: the architecture and the decisions behind it.