Specifications: Pocket Hearing aid Max Sound Output: 1294 dB Max Sound Gain: 60dB 5dB Harmonic Wave Distortion: ?% Frequency Range: 250~3800 hz Input Noise: ?0 dB Battery: 1 x AA battery (included) Working Voltage: dc1.5V Working Current: ?mA Color: As the picture shows Item Size: 6.75 x 4.35 x 1.9cm Note: Adjust volume to the minimum before wearing. Choose an earplug of slightly bigger size to avoid whistler. Increase volume gradually to avoid sudden increase in sound. If you hear a howling, check the ear (silica gel) is appropriate and whether the size of plug is tight, the appropriate choice of earplugs and plugged, make sure no air leakage. Keep the ear plug clean Remove the battery if you don't use it for long time.includes:1 x F-28 Hearing aid 4 x Earplug (different sizes) 1 x AA battery 1 x Screwdriver 1 x User manual