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Optical liquid switch is useful for detection of either absence or presence of water (clear or turbid) or monitor water level. The change in state from presence to absence of water or vice-a-versa triggers relay contact changeover-suitable for control application and also for remote audio/visual indication. The LED illuminated cap provides information on the absence of water locally; OFF - presence, ON - absence. It is a self-contained small device and can be used in any application or process directory employing water service.