More commonly known as cross-device tracking, this describes any method of tracking users and their activity across different devices, despite the fact that they use different devices. To do so, one would have to find identifiers that do not change when the user switches to a new phone, computer or tablet, for instance.  As a result, someone might be able to track an individual’s activity when that person changes from their mobile phone to a desktop computer, for example, even if this person is not logged into any online profiles.