The Sharp Jumbo 4'' Atomic Clock has a built-in receiver that automatically synchronizes itself with the WWVB radio broadcast by the US Government's National Institute in Fort Collins, Colorado. The Atomic clock will always be accurate to within one second. The clock displays the time, indoor and outdoor temperature, calendar, and day of the week. It is a battery-powered main unit with 4 x AA batteries - A sensor, and 2 x AAA batteries (not included). The Wireless outdoor sensor (included) transmits the outdoor temperature to the atomic wall clock.