La Crosse Technology 513-1311OT Jumbo Atomic Digital Wall Clock with Out Temperature, Silver Large, 4.25 inch time display.Monitors IN temperature (F/C).Atomic time and date (manual setting) Automatically updates for Daylight Saving Time (on/off option).12 / 24 Hour time Insert 3 new C batteries(not included) into the clock.Observe the correct polarity Insert 2 new AAA batteries into the outdoor sensor. Observe correct polarity. The red LED will flash when transmitting. After 5 minutes place sensor outside in a shaded location.