The Fisher Labs 9720971000 Headphones with Knob Controls are compatible with Fisher metal detectors and line tracers. Using headphones improves battery life of the device and prevents the sounds from annoying bystanders. It also allows subtle changes in the sound to be more audible, particularly if searching in a noisy location. The model 9720971000 features individual knob controls and utilizes a 1/4 in. jack.