Provides extra protection when the primary AC pump fails due to power outages, when the primary pump fails All models have battery burn out and overcharge. Control device -Reliable low voltage float switch Model 507 has a self contained 10 amp battery recharger. Battery case made from noncorrosive polyethylene. Contains lock strap All systems are fully solid state automatic controllers with alarms, light indicators and have warning systems NOTE: Sump Pump and Battery are not included, as they must be purchased separately. Alarm Off - yellow light indicates the buzzer is currently silenced