With one master key, you can gain access to commercial and residential property. More than 11,500 departments in North America use Knox� products. The Knox System includes UL listed lock boxes, storage cabinets, heavy-duty padlocks and electronic override key switches. Complimentary products include the Sentralok� and KeySecure� Master Key Retention Systems. The system has grown to include locking FDC plugs and caps providing protection to the intake and discharge sides of water-based fire protection systems.