The compatible with Sharp Atomic Wall Clock has a built in receiver that automatically synchronizes itself with the WWVB radio broadcast by the US Government ‘s National Institute of Standards and Technology (NIST) in Fort Collins, Colorado. The compatible with Sharp Atomic Clock will always be accurate to within one second as it receives daily WWVB updates. The Wireless Sensor transmits the outdoor temperature to the compatible with Sharp Atomic Wall Clock. The sensor can be placed anywhere within 100 feet of the receiving unit. NO wire installation needed! Atomic Accuracy: The Atomic clock has a built-in receiver that automatically synchronizes itself with the WWVB radio broadcast by the US Government’s National Institute (NIST) in Fort Collins, Colorado. The Atomic Clock will always be accurate to within one second as it receives daily WWVB updates. Wireless Outdoor Sensor: The Wireless outdoor sensor (included) transmits the outdoor temperature to the Atomic Wall Clock. The sensor can be placed anywhere within 100ft of the receiving unit. The wireless technology means no wire installation is necessary. Note: The wireless sensor is included in the box, separate from the clock. Jumbo 3” Tall LCD Time Display - Easy to Read, Easy to Use, Easy to Set up - Use as either a wall clock, or as a desk clock with integrated stand. Perfect for anyplace in your home. Displays indoor and outdoor temperature - Displays calendar and day of week Battery powered: Main unit 3 x AA batteries - Sensor 2 x AAA batteries (not included)