The atomic clocks that we sell are actually radio-controlled clocks that syncronize with a true atomic clock. Consumer use atomic clocks contain a small antenna which decodes a radio signal from Fort Collins, Colorado (in the continental US) to accurately keep the official time. Set the time zone and the atomic clock will display perfect time. It will also automatically correct itself for daylight savings.

For the consumer a radio-controlled clock is the exact same thing as an atomic clock. An analog atomic clock uses hour and minute hands to represent time, whereas the digital atomic clock uses digital numbers. Nowadays consumer atomic clocks work almost anywhere, although geographic features, weather disturbances, and structural characteristics can affect the strength of the radio signal. Atomic clocks come in all styles – desk, wall, alarm, travel, etc. and typically operate on either one or two AA batteries.

See below for a referance article on what constitutes a true atomic clock.

Atomic Clock
The Columbia Encyclopedia, Sixth Edition | 2008 | The Columbia Encyclopedia, Sixth Edition. Copyright 2008 Columbia University Press

Atomic clock electric or electronic timekeeping device that is controlled by atomic or molecular oscillations. A timekeeping device must contain or be connected to some apparatus that oscillates at a uniform rate to control the rate of movement of its hands or the rate of change of its digits. Mechanical clocks and watches use oscillating balance wheels, pendulums, and tuning forks. Much greater accuracy can be attained by using the oscillations of atoms or molecules. Because the frequency of such oscillations is so high, it is not possible to use them as a direct means of controlling a clock. Instead, the clock is controlled by a highly stable crystal oscillator whose output is automatically multiplied and compared with the frequency of the atomic system. Errors in the oscillator frequency are then automatically corrected. Time is usually displayed by an atomic clock with digital or other sophisticated readout devices.

The first atomic clock, invented in 1948, utilized the vibrations of ammonia molecules. The error between a pair of such clocks, i.e., the difference in indicated time if both were started at the same instant and later compared, was typically about one second in three thousand years. In 1955 the first cesium-beam clock (a device that uses as a reference the exact frequency of the microwave spectral line emitted by cesium atoms) was placed in operation at the National Physical Laboratory at Teddington, England. It is estimated that such a clock would gain or lose less than a second in three million years. The U.S. standard is the NIST-F1, which went into service in 1999 and should neither gain nor lose a second in 20 million years. A fountain atomic clock, the NIST F-1 consists of a 3-foot vertical tube inside a taller structure. It uses lasers to cool cesium atoms, forming a ball of atoms that lasers then toss into the air, much like one would toss a tennis ball, creating a fountain effect. This allows the atoms to be observed for much longer than could be done with any previous clock.

Many of the world's nations maintain atomic clocks at standards laboratories, the time kept by these clocks being averaged to produce a standard called international atomic time (TAI). Highly accurate time signals from these standards laboratories are broadcast around the globe by shortwave-radio broadcast stations or by artificial satellites, the signals being used for such things as tracking space vehicles, electronic navigation systems, and studying the motions of the earth's crust. The accuracy of these clocks made possible an experiment confirming an important prediction of Einstein's theory of relativity. Prototypes of atomic clocks using atoms such as hydrogen or beryllium could be still thousands of times more accurate. For example, researchers at the U.S. National Institute of Standards and Technology have demonstrated an atomic clock based on an energy transition in a single trapped mercury ion (a mercury atom that is missing one electron) that has the potential to be up to 1,000 times more accurate than current atomic clocks.

Bibliography: See F. G. Major, The Quantum Beat: The Physical Principles of Atomic Clocks (1999).
"atomic clock." The Columbia Encyclopedia, Sixth Edition. 2008. Encyclopedia.com. 22 May. 2009 <http://www.encyclopedia.com>.