This is a pretty interesting subject. I hadn’t heard of 2 wire sprinkler installation technology until being prompted to learn from the above posting.
Now I understand and it makes sense for large implementations. Only two wires are needed to go past every valve in the field. What a cost savings when looking at implementing #14 or #12 wire.
This is like the commercial fire alarm panels. Only four wires goes out to all smoke detectors, regardless of location. Each detector is addressed uniquely, such that when it goes off the panel knows exactly which one, perhaps in a sea of hundreds such as in a hotel, without anything but the basic 4-wire connection.