Systems and methods for wirelessly detecting a sold-out state for beverage dispensers

A detection device for detecting that a source is sold-out for a beverage dispenser, the beverage dispenser dispensing from the source via a valve controlled by a solenoid. A circuit board is configured to be positioned on the valve proximal to the solenoid. A detector is coupled to the circuit board, where the solenoid creates a magnetic field when dispensing from the valve, and where the detector detects the magnetic field created by the solenoid and consequently produces an electrical output. A control system is coupled to the circuit board in communication with the detector. The control system is configured to access threshold data and to compare the electrical output of the detector to the threshold data. The control system indicates that the source is sold-out based upon the comparison of the electrical output to the threshold data.