This ultrasonic transmitter for use with the Whisper Ultrasonic Leak Detector provides quick, accurate leak checking in walk-in coolers/freezers, wall and ceiling joints, around doors and windows, ducts, etc. Turn the transmitter on and place it in the enclosed system you need to leak check. If the Whisper detects the ultrasonic frequency generated by the transmitter, you will know the presence and location of the leak.