The official definition of SDI-12 is Serial Data Interface at 1200 baud. Having stated that, SDI-12 is a protocol that was developed within the water resources field to make it easier to determine if a sensor and a data logger were compatible. Instead of having to work through the specifications of the data logger and the sensor for output, input, excitation, wiring, power, programming, etc., all SDI-12 sensors would have just three wires—a serial data line, a ground line, and a 12 V power line.