Grande sonnerie (French, meaning 'grand strike') is a complication in a mechanical watch or clock which combines a quarter striking mechanism with a repeater. On every quarter-hour it strikes the number of quarter hours audibly on a gong, and then the number of hours since the last hour on a second gong. For instance, in a 3 weight Vienna regulator wall clock, at 6:15 it would strike once on a high pitched gong, then strike six times on a lower pitched gong. At 6:30 it would strike twice on the high pitched gong, then six times on the lower pitched gong. At 6:45 three times on the high pitched gong, then six times on the lower pitched gong, and at 7:00 it would strike four times on the high pitched gong, then seven times on the lower pitched gong. You will always know the exact time every fifteen minutes just by listening to the striking. These types of striking clocks are mostly found as French Carriage Clocks, or German three weight Vienna regulators. In addition they can strike the quarters and hours on demand, by activating a repeating mechanism at the push of a button, or the pull of a string.  The term is sometimes used erroneously for a mere quarter striking mechanism.
It is more complex than the petite sonnerie, which merely strikes the hours on the hour and the quarter hours on the quarter, with no repeater function.