A ratchet or rattle, more specifically, cog rattle is a musical instrument of the percussion family and a warning/signaling device. It operates on the principle of the ratchet device, using a gearwheel and a stiff board mounted on a handle, which rotates freely. Variants include the gragger (גראַגער) used in Judaism, the rapach, and the raganella.
The player holds the handle and swings the whole mechanism around. The momentum makes the board click against the gearwheel, producing a clicking and rattling noise. A popular design consists of a thick wooden cog wheel attached to a handle and two wooden flanges that alternately hit the teeth of the cog when the handle turns. Alternatively, smaller ratchets are sometimes held still or mounted and the handle turned rapidly by the player. The mounted ratchets allow for greater control of the duration and timing of the sound. This allows the ratchet to be used like a snare drum, placing sustained rolls in precise durations of time. Dynamics are controlled by the rate at which the ratchet is rotated.
Grager
In Judaism, the gragger (also grogger or gregger; ) is used for the holiday of Purim. The gragger is used every time Haman's name is mentioned during the reading of the Megillah. Because Haman persecuted the Jews, the noise is supposed to symbolically drown out his name (although every word of the Megillah, including Haman's name, must be heard clearly; therefore, the words are often repeated after the sounding of the gragger). The gragger originated in Jewish tradition to help make noise during the reading.
The rattle is used in such compositions as Richard Strauss's Till Eulenspiegel's Merry Pranks and Arnold Schoenberg's Gurre-Lieder.
Up until the early 1970s, this type of rattle was commonly used by fans at soccer and rugby matches in the United Kingdom and was known as a football rattle.
In the 18th and 19th centuries, a policeman's rattle was used by British and Australian policemen to summon assistance.