DGP920B - Data gathering panel with wall mount enclosure and interconnect board.  Each DGP supports 2 card readers, 2 door locks, 2 door switches and 4 alarm inputs. EXP920 - I/O expansion board adds 24 inputs and 24 outputs to a DGP920B.  The EXP920 mounts in the same enclosure, above the interconnect board. ESP000 - Noise suppresser kit prevents electric spikes (noise), from causing damage to DGP electronics.  One suppresser kit is recommended for each door lock on the system. PSA012 - Power supply kit, 12 VDC @ 2 Amps, including wall mount, locking steel enclosure and gel cell battery.  One power supply is required for each DGP920 data collector.