The How & Why Behind Collecting and Storing Device IDs

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The How/Why Behind Storing Device IDs
Amy Fox

In location-based advertising, device IDs are fundamental. These IDs, known as IDFA on iPhones and Android Advertising IDs on Android devices, provide data that can help marketers build a consistent anonymized consumer profile. This are essential for understanding audience behaviors.

More Useful Than Cookies in the Mobile World

In the years before location-based mobile advertising became viable, marketers relied on cookies to learn more about who their customers were. Cookies can still provide a lot of information about user behavior, but they have their limitations. For starters, cookies only work within browsers, which means they only work from website to website. In the world of the desktop, that’s not really an issue, as browsers are still how most of us access the web on a computer.

In the ever growing mobile world however, cookies are less useful. While browsers are still used to access mobile web pages, the majority of mobile time is spent in apps. (In the US, only 8 percent of mobile time was spent in browsers in the last quarter of 2016.) Since apps represent an independent environment, cookies aren’t useful; they can’t follow a user from app to app. Cookies also generally last 30 days or less, whereas device IDs are valid for however long the user keeps his or her phone and doesn’t manually reset it And, since the device ID doesn’t change as a user goes from app to app, tracking this information can provide a wealth of information about customer behavior, helping marketers piece together a more complete picture.

But Are They Safe to Use?

While users can actually change the device ID on their handset, most don’t bother or simply don’t know how it’s done. Even if they are savvy enough to change the ID, there’s not much reason to do so. For one thing, carriers generally will not pass identifiable information on to advertisers. Blis, like most other companies in the digital advertising world, do not directly handle personally identifiable information (PII). That said, customers who are concerned about privacy can easily choose to turn on the “do not track” feature on their phone – as about 15 percent of mobile users do.

However, users should consider that, since their privacy is protected by law, allowing their IDs to be tracked will only improve their digital experiences. Consumers may not think about it today, but it’s actually quite jarring to see ads that are clearly intended for someone else. It’s always awkward (and occasionally insulting) to be shown an ad for anti-aging serum when you’re 25, or an offer for discounted dog food when you don’t have a dog and live in a pet-free building. On the other hand, as a younger woman who loves running, I’d be quite happy to see offers for free shipping on a new pair of trainers.

Useful for Attribution

For marketers obviously, device IDs are vitally important for targeting, but they also play a critical role for attribution. Chains like Starbucks or McDonalds are able to see, for example, how many customers came into a store and made a purchase following their exposure to one of their ads. For them, device IDs are a reliable way to see if online campaigns actually influenced offline behaviour, because they can see if a customer who interacted with a campaign then physically entered a store. If there’s been a bump in revenue after a particular campaign, device IDs make it much easier to attribute that growth to that activity.

Device IDs provide an excellent way for marketers to understand their audiences. Along with other data sources, they can help put the story together, so marketers can see who consumers are, where they go and what’s important to them. And, since the data is both consistent and non-PII, device IDs are not only more accurate than cookies, they’re safe for both consumers and marketers.


As we bring this series of blog posts to a close, I want to urge marketers to keep learning, to ask questions, and to keep an open mind. It’s so important for you to stay educated and become more comfortable with both technology and data. And with the speed with which the industry is accelerating – you’re going to need to be more tech-savvy than ever.

All the channels we use today: social, mobile, television – it’s all converging, and location will be central to everything. So stay on top of all the industry advances and trends, but most importantly, keep learning more. Whatever you learn today is important and useful, but it’s all bound to change – quickly.

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Amy Fox is Head of Product at Blis and is responsible for high level product strategy and development alongside the release of new revenue streams and products into the market. As one of the original Blis employees, Amy has grown her career over the last few years from an entry level role in partner relationships through to heading up both Operations and Product sequentially.

Comments (1)

  • Marcus Brook


    I was with you all of the way up to one point; the last sentence re PII.
    The UK audience has gone mobile and cookies are useless for over 90% of the enormous mobile traffic. Our publishers are seeing far better engagement with their audience and dwell times are far higher too. Moreover, advertisers who use ID’s to target individuals are seeing CTR’s above 0.5% where they get 0.05% on browser based content. (10x better) Device ID’s can help with this. Here’s the BUT….
    Ad tags don’t tend to utilise devise ID’s consistently across content as the publishers still use old cookie based tags in their movie content. But even that isn’ the problem.
    The problem is that on 25th May 2018, you must obtain permission form the “natural person” to use their device ID. Clause 30 of the regulation states this clearly. A €10m fine is applicable for non compliance for each case. Yikes!
    The good news is that this is the biggest opportunity that both advertisers and publishers have for releasing the suffocating grip that the duopoly of Facebook and Google has over our industry, as you illustrate beautifully above. Question is, do we recognise it as such and are we going to do something about it?


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