Check the listing for details. Silent Knight SD500-LIM Line Isolation Module. Condition: New, Made in United States. Listed at 89.99 USD. The Silent Knight SD500-LIM Line Isolation Module is a reliable fire protection equipment manufactured by the brand Silent Knight in the United States. This unit is designed specifically for fire alarms and ensures safety in various commercial and industrial settings. With its model number SD500-LIM, this module is a crucial component in a comprehensive fire protection system, providing peace of mind against potential fire hazards. This item is new. It is overstock from a commercial electrical company. I do not ever sell used items.