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

# Is First Event per Device/User ID

Airbridge identifies first events (e.g. first installation, first purchase) using the below logic. Two types of IDs are used.

## Is First Event per Device ID

DeviceID is provided and used for mobile app events only.

| Device ID | Event Category | Event Time          | Is First Event per Device ID |
| --------- | -------------- | ------------------- | ---------------------------- |
| deviceID1 | Install (App)  | 2020-06-24 17:00:00 | true                         |
| deviceID1 | Install (App)  | 2020-06-25 18:00:00 | false                        |

## Is First Event per User ID

UserID is provided and used for both web and app events. The event category of the first event is applied to the Web + App platform.

| User ID | Event Category       | Event Time          | Is First Event per User ID |
| ------- | -------------------- | ------------------- | -------------------------- |
| userID1 | Order Complete (App) | 2020-06-22 21:36:00 | true                       |
| userID1 | Order Complete (Web) | 2020-06-23 09:00:00 | false                      |

## Additional Notes

* If "Is First Event Per Device" is null: DeviceID is empty or not the right format.
* If "Is First Event Per User" is null: UserID is empty or not the right format.

<link rel="alternate" hrefLang="en" href="https://help.airbridge.io/en/developers/first-event-faq" />

<link rel="alternate" hrefLang="ko" href="https://help.airbridge.io/ko/developers/first-event-faq" />