Abstract: A digital gas sensing system comprises a plurality of satellite subassembly units each including a central processing unit (CPU) and a plurality of "intelligent" sensors connected to the satellite subassembly units by a single pair of leads. The satellite subassembly units communicate to the sensors in a code having a predetermined number of digital bits. Each sensor has internal "intelligence" and recognizes its own unique address and responds to the satellite subassembly unit in a predetermined code that varies from the satellite subassembly unit code by one parity bit. This arrangement makes it possible for other sensors to distinguish between transmissions from the satellite subassembly unit and transmissions from other sensors. The net result is that the system is able to operate very reliably using only two leads to connect all of the sensors to the satellite sub subassembly unit thereby greatly reducing the wiring and installation costs of the system.