求关于闹钟的2`3句话

History of the Alarm Clock
The first mechanical clocks were made in the 14th century, and were large monumental clocks. Household clocks were in use by 1620 and some of them had alarm mechanisms. The alarm is simple in concept, typically having a cam that rotates every 12 hours. It has a notch into which a lever can fall, releasing a train of gears that drives a hammer, which repeatedly hits a bell until it runs down or is shut off (many alarms have no shutoff control).

The earliest alarm clock I found reference to is a German iron wall clock with a bronze bell, probably made in Nuremberg in the 15th century. This clock is 19 inches tall and of open framework construction. It needed to hang high on the wall to make room for the driving weight to fall. Other alarm clocks from the 1500's are in existence. See “The Clockwork Universe, German Clocks and Automata 1550 - 1650,” Maurice and Mayr, 1980, Smithsonian, Neale Watson Academic Publications, New York.