Check the listing for details. System Sensor HWL-LF-BP10 Bulk Pack 10 Units - Same Day Shipping (SEALED). Condition: New. Listed at 568.10 USD. System Sensor HWL-LF-BP10 | Same Day Shipping (SEALED) HWL-LF-BP10 SYSTEM SENSOR Pack with 10 units! The L-Series offers the most versatile and easy-to-use line of low frequency sounder and low frequency sounder strobes in the industry. With white and red plastic housings, listed for wall and ceiling mounting, L-Series Low Frequency can meet virtually any application requirement.The low frequency sounder and low frequency sounder strobes were 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% and is of a square wave tone. Like the entire L-Series product line they include a variety of features that increase their application versatility while simplifying installation. All devices feature plug-in designs with minimal intrusion into the back box, making installations fast and foolproof while virtually eliminating costly and time-consuming ground faults.