Was this an universal tool throughout medieval Europe, or were there many alternatives by country-to-country basis? Say, drums?
The US Army claim that the bugle call they sound during their end-of-day Retreat ceremony was composed 900 years ago during the Crusades. The US adopted it from the French Army, who have a history of using horns going back to the Battle of Bouvines in 1214, where trumpets sounded the signal for the victorious charge when Philip Augustus of France defeated Otto IV of Germany. This is the earliest known use of the horn after the Romans.
Drums and bugles/trumpets co-existed in European armies even into the days of firearms which might have been expected to make hearing drum signals more difficult. The sound-carrying properties of military drums were improved in the C14 by snare drums coming into use with gut strings or metal wires rattling against the lower drumhead.
As well as signalling, both types of musical instrument were also used for intimidation. Local loud wind instruments were also put into service, I do not know if any European army used them to the exclusion of bugles or trumpets. (The Irish bagpipes called in English the 'Great Irish Warpipes' were first used a little later, in the late C16.)