Simplex 4100 637-996 Audio Decoder 566-223 Module This item is used, untested and pulled from a working environment. It does say that this item is a 4100 Digital Audio Decoder Module 566-223. Please see photos for what you see is what you will receive. Used Simplex 4100 Digital Audio Decoder Module Assy 637-996 featuring 566-223 decoder board (Service No. 743-559) with installation instructions 579-779 Rev A. Essential voice evacuation component decodes digital audio messages for zoned alert/evac tones through 4100 series amplifiers. Direct-fit replacement for legacy 4100U/4100ES panels in commercial buildings, schools, hospitals requiring voice fire alarm systems. Item Specifics: Brand: Simplex (Johnson Controls) Part Numbers: 637-996 Assy (566-223 Module), Service No. 743-559 Type: 4100 Series Digital Audio Decoder Module Installation Instructions: 579-779 Rev A Application: Simplex 4100/4010 voice evacuation fire alarm panels Mounting: Panel/rack mount with ribbon cable connectors Power: 24 VDC fire alarm system power Features: Digital message decoding, zoned audio distribution Condition: Used, untested SHELF: 14 bin 3 AP