The Signature Electronic Stethoscope is Equipped With a Built-In Computer Chip. Through this chip, aphonic and resonance effects are eliminated, and audio frequency can be divided into three selective modes; Standard Bell, Diaphragm, and Extended Diaphragm. Electronic amplifying system adjusts for eight different volume levels. Automatically starts in the sound collection mode and volume mode. Auto shut-off saves the battery life after two minutes of non-use. Adjustable binaural to ensure maximum ear comfort. Includes batteries. Manufacturers Three-year limited warranty.