Many restaurants serve fountain drinks made of mixed syrup and CO2. Servers and managers monitor syrup levels to ensure quality beverages with manual techniques, such as observing the color of the drinks, lifting the syrup canisters to judge weight, and visually observing containers. In a busy establishment, syrup levels often run low or completely out before a supervisor or server notices, causing poor customer service, poor quality drinks, or interrupted service.
To remedy this problem, six undergraduates students developed the SOS, or Syrup Out Signal. SOS monitors fluid levels in CO2 canisters and syrup boxes and alerts restaurant staff when the ingredients reach low levels. With syrup in the tubing, the circuit generates a steady voltage output. But when air replaces the syrup in the line, the voltage lowers. This sudden change in voltage causes a radio transmitter to signal a receiver, which supplies current to a light-emitting diode and turns on a warning light, alerting the user to low syrup levels.