Lawn irrigation controllers are electronic devices used to control automatic sprinkler systems.  Most controllers incorporate a means of controlling the time and duration of watering, which areas are watered and at what times.  Most modern irrigation controllers also offer the ability to incorporate rain sensors or other environmental monitoring equipment into the controllers programming, allowing the irrigation controller to select times or dates when there is no need in activating the lawn sprinkler system.  This saves on water consumption as well as preventing accidental watering during periods of natural rainfall.