In-ear monitors are very common for drummers now, they usually hear either a click track (a metronome) to keep them in time if they need to follow specific lighting and effects cues, or a selected mix of the band's sound for the same reason.
In-ears are far less obvious than headphones - times move on of course - and they simultaniously block out all other external noise. Most drummers have them custom made for ther own ears, but youhave to have considerablt trust in the mintor engineer because a balst of sonic feedback could cause instant and irreperable hearing damage.