Minute repeater is simply an acoustic complication in mechanical watches that is executed with a press of a button at the side of the case. After starting repeater mechanism, the actual time is audibly chimed on demand. The time is chimed with hammers hitting steel resonant wire, leading around the mechanism and parallel to the case. There are many types of repeaters, starting from the simplest mechanism, that strikes only hours, through more complicated, with different tones for hours and minutes.
The assumption was to create a watch to be used in darkness and as an aid to the blind.
The first watch with minute repeater was constructed in 1749 by Pierre-Joseph de Rivaz, although it was first proposed by Antoine Thiout ca. 1740.
Minute repeater is considered one of the most difficult horology complications, with tourbillon or equation following suit.
The main photo shows an example — movement in Vacheron Constantin, calibre 2755.