Step 1: Turn the Invisible Hearing Aid switch on by moving the dial to the ON section Step 2: Make sure the volume dial is set to the minimum (lowest level) Step 3: Insert the Invisible Hearing Aid inside your ear Step 4: Adjust the volume until you hear a sound.Specification Max sound output: 120dB Sound gain: ≥30dB Total harmonic wave distortion: <1000Hz≤10% Frequency range: 250-3800Hz Input noise: ≤50dB Voltage: DC1.5V Current: ≤4mA Color: As picturesBattery InstallationGently open the battery compartment cover at the back of the device. Put AG13/LR44 battery into the battery compartment in the right direction, then close the battery compartment.Package 1xMini Hearing Aid 2 x AG3 Button Cells 1 x Instruction Manual 1 x Case 2 x Units of the earplug of different size Brand No Brand SKU 100824142_NP-1021328834