Petite sonnerie is an automatic striking mode that chimes the quarters as they pass without repeating the hour at every quarter change. This seemingly subtle distinction cleanly separates petite from grande sonnerie: in grande, every quarter hour brings with it a repetition of all the hours struck up to that moment; in petite, the hours sound only at their exact striking, and the quarters follow without replay.
The mechanism works en passant, meaning it activates autonomously without the wearer's intervention, unlike the minute repeater which instead responds to a pusher or the crown. This autonomy has a precise cost: higher energy consumption compared to silence or the minute repeater, with measurable reduction in power reserve. For this reason, almost all movements with striking complications integrate a selector — sliding, coaxial pusher, or on the crown — that allows switching between grande sonnerie, petite sonnerie, and silence.
From the bench I've seen enough pieces with this complication to understand that petite is often the mode for daily use: it consumes less than grande, doesn't saturate the ear, remains discreet. Grande sonnerie is impressive for five minutes; petite you live with all day.
Among the houses that have published technically relevant interpretations: Audemars Piguet in the Code 11.59 Universelle with selection via the crown at 3 o'clock, Chopard in the L.U.C Grand Strike with sliding selector, Blancpain in the Grande Double Sonnerie which uses four notes instead of the traditional two. Philippe Dufour built his reputation partly on the Grande et Petite Sonnerie, one of the few movements where manual finishing extends to the striking train wheels. In total, the manufacturers capable of producing a movement with complete and reliable striking can be counted on the fingers of two hands, perhaps one.
The abbreviation PS also appears in other contexts: in some calibers it indicates petite seconde, meaning the seconds in a subdial separate from the central hand. The term should not be confused with petite tapisserie, which is a decorative guilloché motif on Audemars Piguet dials and has no relation to the striking mechanism.