The JS Products Steelman EngineEAR Stethoscope, No. 65001, consists of an ultra-sensitive microphone and amplifier providing a full range of sound with no missing frequencies. The professional noise-canceling headphones isolate sound with no unwanted sounds bleeding in. Using the flexible shaft with the metal probe for picking up sounds and vibrations, users are able to pinpoint noises and locate worn bearings and bushings, noisy valves and lifters, broken or worn gear teeth, faulty fuel injectors, wind or air leaks, and annoying squeaks and rattles. The stethoscope comes with one 9V battery.