L-Series low frequency sounders include a variety of features that increase their application versatility while simplifying installation. They are designed to address the NFPA 72 sleeping space requirements that require a low frequency notification appliance that operates within frequency range of 520 Hz +/-10 Percentage and is of a square wave tone. These devices feature plug-in designs making installations fast and foolproof while virtually eliminating costly and time-consuming ground faults. Installers can also easily adapt devices to a suit a wide range of application requirements with 24 V operation and a rotary switch for 520 Hz low frequency sounder tones.