Abstract: An ultrasonic non-destructive testing system is disclosed wherein electrical signals from a search unit are displayed to visually represent reflections of ultrasonic waves occurring within a work piece or test material. The system includes means for generating an alarm or warning signal informing the operator that an ultrasonic echo has occurred which indicates a possible defect. The alarm causes the display screen to be flashed "on" and "off" at a slow rate in response to a detected ultrasonic echo which exceeds the critical level. The flashing screen signals the operator to make a closer visual inspection of the display, which appears intermittently as the display is flashed on and off.