Captures Sounds Typically Difficult to Identify Eliminates aphonic and resonance effects for enhanced audibility. Audio frequency can be divided into 3 selective modes: Standard Bell 2 Diaphragm 3 Extended Diaphragm Electronic amplifying system offers 8 different volume levels. Automatically starts with the last used sound collection and volume mode. Features automatic shut-off after 2 minutes. Includes 3 LR44 mercury batteries. Flexible binaural control and a 3-year limited warranty.