Silent Knight SD500-ARM 2-Wire Smoke Module USEDSD500 ARM USED addressable relay modules add two Form C contacts to the Farenhyt addressable system. The contacts are rated at 2A at 30V DC or 0. 6A at 120V AC. SD500 ARM addressable relay modules allow you to control a wide variety of normally open and normally closed applications, including elevator recall, door closing, fan operation, and auxiliary notification. Because the relay modules are addressable, these applications can be located at any