What type of ID would you use for tracking a user's behavior across multiple devices?

Using a Cross-device ID is the most effective way to track a user's behavior across multiple devices. This type of ID is specifically designed to link a user's activity across various platforms and devices, such as smartphones, tablets, and computers. By utilizing Cross-device IDs, companies can create a unified view of user interactions, allowing for more accurate data analysis, personalization, and marketing strategies.

In contrast, a User ID typically designates a unique identifier for a person, but it does not inherently account for their multiple devices. A Cookie ID is mainly used to track user behavior on a single device through browser cookies, which can limit its effectiveness in cross-device analytics. A Session ID focuses primarily on a specific interaction period rather than longitudinal tracking, as it resets with every new session initiated by a user. The Cross-device ID's ability to consolidate data from different environments ensures comprehensive tracking and insights into user behavior.