@polychrome CSS @media queries mostly, wouldn't mind taking a look if you have a concrete casus?
@f0x I'm probably going to have to give in and use some minimal JS to guess by agent strings.
@polychrome I think it's the viewport meta tag that helps with this
https://developer.mozilla.org/en-US/docs/Mozilla/Mobile/Viewport_meta_tag
@f0x had some trouble deciphering how to recognize when a device is mobile using @media queries because it only gives me resolutions and orientation, both of which not really distinct from a PC display