Use our surface mic to listen for faint sounds through virtually any solid surface. The probe features a built in contact element and has an internal automatic gain control that does not need constant adjustment. This microphone is designed to convert minute vibrations to voice band audio that can be received by headphones or secondary measurement equipment. Specifications: ¥ Internal automatic gain control ¥ Built in contact element ¥ Connects to any standard tape recorder ¥ Uses 9V battery ( not included) ¥ Recorder output compatible with audio spectrum analyzers Includes: ¥ Ear Phones ¥ Instruction manual SIZE: 3 3/4" x 2 3/8" x 1"