The Dual Channel Smoke Detector (DCSD) from Advanced Aircraft Extinguishers, Ltd contains both the A and B channel within one unit.
One unit per enclosure. Each channel (A and B) has separate and autonomous power and ground, and inputs and outputs.
The Dual Channel Smoke Detector part available currently from Advanced Aircraft Extinguishers, Ltd is shown below.
TFC13-0024-3, Smoke Detector, Dual Channel