What is a device ID?

A device ID is a unique, anonymized string of numbers and letters that identifies every individual smartphone or tablet in the world. It is stored on the mobile device and can be retrieved by any app that is downloaded and installed. Apps typically retrieve the ID for identification when talking to servers. Recent updates, such as Apple’s App Tracking Transparency (ATT), introduced with iOS 14.5 in April of 2021, require explicit user consent to access the device ID on iOS.

This privacy-centric framework has spearheaded an industry-wide move toward aggregated measurement and privacy preserving attribution and campaign optimization. Google’s equivalent, Privacy Sandbox on Android, is also expected to significantly reduce reliance on device IDs for Android.

The two most common device ID types are Apple’s identifier for advertisers (IDFA), the device ID for iOS, and the Google Advertising ID (GAID), the device ID for Android. Both work in the same way, functioning as a unique identifier that can be used to connect a device to ad campaigns, app installs, and in-app events. Device IDs have most commonly been used in mobile advertising to process information on user preferences, create segments, and provide personalized ad and app experiences.

• iOS: The IDFA is an eight digit code followed by a dash and three sets of four digits. Since the introduction of ATT, users can opt-in or opt-out of sharing this ID with app developers and advertisers. Users are opted-out by default. To gain the opt-in, an app must serve a prompt to the user, and they must select “Allow Tracking”. Users can configure their opt-ins and opt-outs for each installed app under Tracking in Settings. It’s also possible to toggle off “Allow Apps to Request to Track,” meaning that developers would not have the option to serve the prompt at all.
• Android: The GAID, also known as the Android advertising identifier or Android ad ID, and formerly named the Android ID, Android Device ID, and Android Advertising ID (AAID), is Google’s unique device identifier for Android devices. The GAID is also made up of an initial eight character code, followed by a dash and three sets of four digits. Unlike the IDFA, all of the GAID’s letters are lowercase. The GAID can be accessed and reset within an Android device’s privacy settings. From Android 12, the GAID is zeroed out for users who opt-out of ad personalization, and from Android 14 onward, it’s possible to customize ad settings, or to completely remove the GAID. Privacy Sandbox on Android, due for full rollout in 2025, will further reduce advertisers’ need to work with the GAID.

Device IDs are the easiest way to identify devices and measure campaign performance, as they allow for granular insight into user journeys, behavior, and preferences. This not only enables more personalized advertising, but improves cohort creation, segmentation, and the facilitation of high-powered predictive analytics.

If a publisher is able to access a device ID, they can see whether that device viewed an ad, installed an app, and how they used that app. This makes it possible to understand which ad groups, creatives, channels, and partners are sending the highest value users. Although next generation measurement tools and solutions make it possible to gain campaign insights by working with aggregated data, the granular data captured using device IDs can drastically improve the quality of the modeling and predictions performed by the next-gen technologies. In short, the more first-party data you’re able to gather, the better your entire analytics and optimization strategy will be.

Device IDs are used for identifying and tracking/measuring mobile devices, enabling personalized advertising, user behavior analysis, and cohort creation. They help in attributing app installs and in-app actions to specific ad campaigns. This makes it easy to optimize marketing strategies and improve ROI. By matching a device ID to user actions across channels, a clear journey is graphed, including when users convert, and when they churn.

Some of the key ways device IDs can be used, include:

• Attributing app installs: Determining which campaigns led to installs/downloads.
• Measuring in-app events: Insights into user actions within an app, such as purchases and level completions.
• Personalized advertising: Delivering tailored ads based on user behavior and preferences.
• User segmentation: Creating user groups based on behavior, geography, or other criteria.
• Fraud detection: Identifying and preventing fraudulent activities.

A device ID is generated by the device’s operating system and—where relevant consent is granted—is accessible to apps upon installation (the first launch after download). It serves as an anonymous identifier that helps apps communicate with servers, measure user interactions, and deliver personalized content without revealing personal information. Following the installation of an app, if the device ID is available, it can be used to perform attribution. Via attribution, the device ID can be linked to previous and future activity.

For attribution of an event to a specific ad campaign to work, the MMP’s SDK needs to match the two data points. An attribution will only take place if the event is triggered within the attribution window.

Given the complexity of user privacy and the constantly evolving frameworks and regulations, many users are either not aware of what a device ID is, don’t know how to find their device ID, or simply want to know how to check a device ID on iPhone and Android devices. Finding a device ID, resetting it, or restricting access to it, are all possible Android. On iOS, you can view and manage IDFA settings.

• iOS: Go to Settings > Privacy & Security > Tracking to toggle on and off which apps can access your IDFA. You can also turn off 'Allow Apps to Request to Track’.
• Android: Go to Settings (or Google settings) > Security & Privacy > Privacy > Ads to find and reset your GAID, and manage/customize personalization preferences.

Access to—and dependency on—device IDs to perform attribution is decreasing. As the mobile advertising industry moves toward a status quo of privacy-centric measurement, teams need to adapt to new attribution and campaign optimization methods. Working with tools and frameworks that enable strategic and scalable growth without relying solely on device IDs is the most sustainable way forward. Optimizing for maximum consent is also advised, however, as the more granular data that can be gathered from device IDs, the better.

While the move toward working with aggregated data and methods like incrementality, predictive analytics, and media mix modeling is essential, traditional attribution and consented device-level data are invaluable in informing these next-generation solutions and the machine learning algorithms that power them.

To learn more about Adjust’s AI-driven, next-generation solutions for measurement and campaign optimization, see Recommend or request a demo today.