---
title: "External ID"
slug: "mobile-checkin-app-external-id"
updated: 2026-03-30T14:56:09Z
published: 2026-03-30T14:56:09Z
canonical: "docs.blackthorn.io/mobile-checkin-app-external-id"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://docs.blackthorn.io/llms.txt
> Use this file to discover all available pages before exploring further.

# External ID

Simplify the check-in process for large, free Events with the Mobile Check-in app’s External ID feature. Users can quickly check in large numbers of unregistered Attendees, ensuring an accurate and real-time Attendee count.

## Prerequisite

The External ID feature only works with free Events.

## Setup

The new **BT External ID** field is located on the Contact object. You will need to add it to the Contact page layout. This field is used by the Mobile Check-in app to identify Contacts with a matching ID that is found in a non-Blackthorn QR code.

![External ID Feature](https://cdn.document360.io/f977eec0-500f-40a3-b663-724a51f78075/Images/Documentation/External%20ID%20Feature.png)

**Complete the following steps before attempting to use the External ID feature.**

1. Determine where the individuals/students within your organization will store or access their unique QR codes.
2. Create a Contact record for each individual/student within your organization. The following fields are required:
  - **First Name**
  - **Last Name**
  - **Email**
  - **BT External ID**
3. Populate each **BT External ID** field with a unique ID.
4. Use the **BT External ID** value to generate a unique QR code from a website such as [The QR Code Generator](https://www.the-qrcode-generator.com).
5. Provide individuals/students with their QR codes.
6. Upgrade the Mobile Check-in app to the newest version.

**Permissions**

New installations include permissions for the **BT External ID** field. Existing users must update their permission sets.

### BT External ID QR Codes and Pre-registered Attendees

Matching and Duplicate rules will dictate whether scanning a **BT External ID** QR code will check in a pre-registered Attendee or create a new Attendee record.

If a Contact pre-registered for an Event using Attendee details (name, email, etc.) that match their Contact record (per org Matching and Duplicate rules), scanning their **BT External ID** QR code will update the existing Attendee’s **Attendance Status**.

However, if a Contact pre-registered for an Event using Attendee details (name, email, etc.) that do not match their Contact record (per org Matching and Duplicate rules), then scanning their **BT External ID** QR code will create a second Attendee record with **Attendance Status** = “Attended” that is related to the same Contact.

## At the Event

1. Using the Blackthorn Mobile Check-in app, select the Event from the Event listing page.
2. Press the **Scan** button to scan the unregistered person’s QR code.
3. The user will see the New Attendee page with the prepopulated Contact information.
4. Tap **Save**. If the Attendee record already exists, the user will be able to check in the attendee.

A new Attendee record will be created with the following fields already populated.

- **First Name**
- **Last Name**
- **Email**
- **Registration Status** = "Registered"
- **Attendance Status** = "Attended"