Shop Citizen Atomic Timekeeping watches. Combined with our proprietary light powered Eco-Drive technology, when owning a Citizen Atomic Timekeeping watch you will get precise time powered by any light source. A signal containing the precise time, day and date, measured by an atomic clock accurate to one second every 20 million years, is sent directly to the watch using standard radio waves. This signal is picked up overnight by the timepiece which automatically adjust the date and time.