Aprilaire protocol adapter for communicating thermostat system. Used in conjunction with any of the 8800 series communicating thermostats and 8800 series communication distribution panels. Requires use of 8820 software. This device plugs into the back of your computer in a serial port and enables the Aprilaire home & business automation system to be operated and programmed from your on-site IBM compatible PC. Can handle up to 32 Aprilaire communicating thermostats.