BJ Enterprises Sentry Overfill-Guard Tank Alarm combines a wall-mounted, battery-operated Sentry tank alarm with an Overfill Guard tank gauge to provide audible and visual warning of an imminent tank overfill. The Overfill Guard is a large, visual sight gauge that will indicate with a highly-visible orange indicator if a tank is approaching overfill status, with a 4-window glass display that is easily read from any direction, while the 2-piece Sentry unit indicates an imminent overfill by sounding a 103-decibel siren, with a control panel that can be mounted almost anywhere for easier accessibility. When activated to an alarm condition, the Sentry will sound its built-in siren for up to 4 days on a fresh 9-volt battery, and the Overfill Guard unit comes with a nickel-plated brass chain that is field-adjustable to 24 in depth.