The R9100 is a handheld ultrasonic leak detector that converts the inaudible high-frequency sound produced by escaping gas, air, vacuum, or fluid at a leak point into an audible signal a technician can hear and pinpoint. It operates at a 40 kHz detection frequency, includes an adjustable sensitivity control plus both LED and audible ticking alarms, and comes with headphones for use in noisy industrial environments. Powered by two 9V batteries, it's commonly used to locate leaks in compressed-air lines, refrigeration/HVAC systems, and pressure or vacuum equipment.