As machines and equipments have become more complex and increasingly automated, and with the advent of microprocessor control, the role of the human operator has changed from that of an active controller to a decision maker and manager, a shift from active to supervisory control. The purpose of this study was to develop an efficient supervisory alarm system by using fuzzy sets to evaluate and improve the performance of supervisors. There are two input variables: fuzzy set, which represents the linguistic notion “hit” when supervisor action is needed, and the fuzzy set Ñ, which represents the linguistic notion “false alarm” when no action is needed. An alarm signal was produced by the fuzzy system for reminding participant's attention. According to the results, the alarm was adapted to call the operator’s attention when a situation needed action to improve the supervisory performance. The results also show that the effect of the fuzzy alarm system for improving supervisory performance is significant.