Seconding @danims1's answer. Adobe collects a lot of information automatically, and a lot of that information is pulled from the User Agent (so you won't see it specifically tracked in your tracking calls).
Things like:
- Device
- Device Type
- Operating System
- Operating System Type
- etc
You shouldn't need to do anything special. Now, in addition to this, we have a responsive website, and I also track the "breakpoint", since we know that computers with smaller resolution will get a "tablet" experience, or people can re-size their browsers for split screen and get the "mobile" experience... or people on Android devices using Chrome can use the "show desktop" option, and get the full resolution of their phone so that they see the desktop experience...
I find the breakpoint tracking is more helpful in determine how features are being used, since the display and the usability of those features is driven by the breakpoint and not the actual devices...
I normally just use JS to get the window.innerWidth and check it against the known widths used by our developers... and if you have multiple breakpoints, like mobile portrait, mobile landscape, tablet portrait, tablet landscape, desktop, large desktop, etc... you can account for all these variations.
