:::{note}

Using external device IDs can produce different results depending on your setup. If you want to use them, contact your Adjust representative. They will talk you through the best approach for your use case.

:::

An external device identifier is a case-sensitive, custom value that you can assign to a device or user. They can help you to recognize users across sessions and platforms. They can also help you to deduplicate installs by user so that the same user isn't counted multiple times.

You can also use an external device ID as a custom identifier for a device. This can be useful if you use these identifiers elsewhere and want to keep continuity.

You need to set your external device ID before you initialize the Adjust SDK. This is because the SDK sends this information at launch to create a device record. If the external device ID is not available until a user has logged in, it will not be available to the Adjust SDK at launch. 

## [SDK requirements](sdk-requirements)

* [iOS](https://dev.adjust.com/en/sdk/ios/configuration#set-external-device-identifier), [Android](https://dev.adjust.com/en/sdk/android/configuration/#set-external-device-identifier), [Unity](https://dev.adjust.com/en/sdk/unity/configuration#set-external-device-identifier), [Corona](https://github.com/adjust/corona_sdk): v4.20.0
* [Adobe AIR](https://github.com/adjust/adobe_air_sdk), [Cordova](https://dev.adjust.com/en/sdk/cordova/configuration#set-external-device-identifier), [Xamarin](https://github.com/adjust/xamarin_sdk), [React Native](https://dev.adjust.com/en/sdk/react-native/configuration#set-external-device-identifier), [Flutter](https://dev.adjust.com/en/sdk/flutter/configuration#set-external-device-identifier): v4.21.0
* [Cocos-2dx](https://dev.adjust.com/en/sdk/cocos2dx/configuration#set-external-device-identifier): v4.22.0
* [Titanium](https://github.com/adjust/titanium_sdk): v4.23.0
* [Web](https://dev.adjust.com/en/sdk/web/configuration#set-external-device-identifier): v5.1.0

## [Use cases](use-cases)

External device identifiers can be useful in the following scenarios:

1. If you want to deduplicate installs by user so that the same user isn't counted as multiple new installs.
2. If you currently use custom IDs for devices and you want to continue using these for reporting.
3. If you want to be able to recognize users across different devices and platforms.

## [Importing external device identifiers](import-external-device-ids)

If you are moving to Adjust from a different system, you can import your external device IDs as part of your setup. Your Adjust representative can help you with importing this data. You can also check our [migration guide](/en/article/migration-guide-suite) for more information.
When a logged in user then updates their app to a version containing the Adjust SDK, the external device ID will be available. This will allow you to continue recording users using your identifiers from day one. 

## [FAQs](faqs)

+++>
### [Can I send external device IDs in S2S events?](server-to-server-events)

Yes! You can send the external device ID as part of [server-to-server (S2S) events](/en/article/server-to-server-s2s-integration). Use the following format to send the information: `external_device_id=your_defined_id`.

===
### [Are external device identifiers available in cloud storage uploads and server callbacks?](cloud-storage-uploads-callbacks)

If you want to use the external device ID in your business analytics, you can pass it as a session callback parameter. See our guide to [custom callback parameters](/en/article/custom-callback-parameters) for more information.

You can use the `{external_device_id_md5}` placeholder to return the hashed external device ID in cloud storage uploads and server callbacks. See our [placeholders list](/en/marketer/placeholders) for more information.

+++<

An external device identifier is a custom value that you can assign to a device or user.

External device identifiers

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