A bicycle bell is a percussive signaling instrument mounted on a bicycle for warning pedestrians and other cyclists. The bell is a required piece of equipment in some jurisdictions. They are usually mounted on the handlebars and thumb activated. The bicycle bell was invented by John Richard Dedicoat, and patents for bicycle bells appear as early as 1877. The most common bells are actuated by a thumb-operated lever that is geared to rapidly rotate two loosely slung metal discs inside the bell housing. Said discs repeatedly rattle and strike the bell to produce a sound not unlike that of an electric bell. Simpler types also exist, with a spring-mounted external clapper that produces a "ding-ding" sound when the clapper is pulled with a finger and released.