Ultrasonic flowmeters and accessories determine flow rate through the wall of a pipe by emitting an ultrasonic signal and reading the acoustic reflection of that signal. Ultrasonic flowmeters process and display the data collected by the detectors. Ultrasonic flowmeter detectors emit the ultrasonic signal and recieve the acoustic reflection resulting from the emission. Ultrasonic flowmeter detector accessories enhance the signal strength observed through the pipe wall or enable the flowmeter to activate a switch when the flow rate reaches a set point.