Door Ajar Light is perfect for use with areas like walk-in coolers, freezers and security doors or window that must remain closed. Instant alerts when the door you need to be closed is open! Allowing for quick response to ensure safety and product damage stays at bay. A simple set of dry contacts turn on the light. Uses (2) standard D-Cell Alkaline batteries (INCLUDED). Bright red flashing light alerts to possible danger. Simple to understand, test and use. No complicated writing or installation required.