The IS-SS is a stainless steel, flush mount audio only door station and is both vandal and weather resistant. It connects to the IS-CCU, IS-SCU or IS-RCU using CAT-5e/6 cable. There is a built in dry contact for door release (24V AC/DC, 500mA). The IS-SS is powered by the system. The IS-RS is a handset style, wall mount, audio only sub station. It connects to the IS-CCU, IS-SCU or IS-RCU units using CAT5e/6 cable. It can be used hands-free with the internal speaker or can be tied to an external 8 ohm speaker. The IS-RS is powered by the system.