Mobile and desktop audiences are built using different technologies:
- Desktop tactics "cookie" the user. Place an audience pixel on your landing page to capture desktop users.
- Mobile tactics collect device IDs. For mobile tactics, you don't need to place a pixel anywhere.
If you're managing both mobile and desktop audiences and want to track the counts of users separately, create one audience for mobile and another audience for desktop. Be sure to name them so you can clearly tell which audience is mobile and which is desktop—you'll need this later when you're targeting to the audiences.
By building separate lists, you keep track of how many users are in your mobile audience pool and how many are in your desktop audience pool.