The present invention relates to a data signal monitoring system for monitoring data signals in a data wire without interrupting data signal flow. In the illustrative embodiment, the data signal monitoring system is connected to the data wires between a fuel dispenser and the the dispenser control console. The design is such that the data signals flow into the monitoring system without interrupting the communication between console and dispenser. The monitoring system interprets the data and analyzes pump status and commands. The data signal monitoring system translates the physical signals in the wire into serial signals which are sent to a microprocessor in the monitoring system for processing. The microprocessor then controls other electrical devices from information extracted from the communication between the pump and console. Such electrical devices include a price sign displaying the price of the fuel and an audio message system which is activated when the pump nozzle handle is lifted.