If you believe some authors, clocks in one form or another have been around since as long ago as 4,000 BC. Possibly the old instruments to measure time were water clocks and sundials, but where and when they first existed is not actually known, although some records indicate that water clocks may have been invented in Egypt in around 1,600 BC. The water clock was either inflow or outflow. Outflow clocks were basically a bowl which was filled with water with a tiny hole which let the water drain out slowly. Lines were drawn on the bowl which indicated the passing of a certain amount of time.

An inflow water clock worked in similar fashion except that water flowed into the container and an observer could tell the passage of time as the water reached each line in the bowl. Another similar method of telling time was the hourglass where sand pours through a fine hole in the glass. When the upper chamber containing the sand empties, the hourglass is turned upside down and the process begins over again.

Sundials, of course, tell the time by the passing of a shadow created by the gnomon on to the base plate as the sun passes through the sky. They are not much use on a cloudy day.

The very first mechanical clocks appeared around the 13th century in Europe and kept time with oscillating timekeepers like balance wheels. Strictly speaking, the word "clock" was used for a striking clock, while a clock which did not strike the hours was a timepiece. However, today anything which keeps the time is known as a clock, except for those carried or worn on the person which are called watches. Spring-driven clocks arrived in the 1400's and then in 1656 came the invention of the pendulum which improved accuracy. This was invented by Dutchman Christiaan Huygens who worked out the mathematical formula that related the time to the length of the pendulum which was 39.1 inches to a second.

The grandfather clock, or longcase clock was first built in England in 1670 by William Clement who also invented the anchor escapement which was an improvement on Huygens' crown escapement. Just five years later, Huygens and Robert Hooke invented the hairspring which controlled the oscillating speed of the balance wheel, and this was what made possible the pocket watch. The minute hand was added to the clock by Londoner Daniel Quare and then the second hand was introduced. Either Quare or Edward Barlow invented the repeating clock which chimes the number of hours in 1676.

Fast forward a couple of hundred years and in 1880 the piezoelectric properties of crystalline quartz were discovered by Pierre and Jacques Curie which led to the first crystal quartz oscillator being built in 1921 by Walter Cady. Six years later, the first quartz clock was built by J. W. Horton and Warren Marrison at the Bell Telephone Laboratories in Canada. The time standard of the US was based on quartz clocks from 1929 to the 1960's when it changed over to atomic clocks. Seiko produced the first quartz wristwatch in 1969 and today they are everywhere.

Of course, just about every home today has a clock and many have several. Some people like wall clocks and you can now get illuminated wall clocks as well, which perform two functions. In some cases, the illumination is merely used as a decoration for the clock or to enhance its' readability, while in others it serves to add extra light to a room during the hours of darkness.