In Ear Hearing Aid Elderly Amplifier Device Plastic Wireless Deafness Ear Care Tools Item Type: In-Ear Hearing Aid Material: Plastic Power Supply: 1 x LR41 button battery (not include) 1. Maximum Sound Output: 110±5dB 2. Sound Gain: ≥30dB 4. Total Harmonic Distortion: ≤10% 5. Frequency Range: 300HZ-4000HZ 6. Input Noise: ≤40dB 7.Voltage: 1.5V Instructions: 1. Open the battery box, put in the corresponding battery, and cover the battery box tightly.(Note: Open the battery box, the product will stop working, completely close the battery box, it will start working.) 2. Insert the earplug into the hearing aid, put the hearing aid into the ear, move it up and down to make sure its position is correct, adjust the volume to get a clear sound 3. If you feel the sound of whistling, please confirm whether you plug the earplugs tightly, or whether you use earplugs of appropriate size. 4. When you stop using the hearing aid, please remove the battery or turn off the power of the hearing aid. (Note: Please make sure the hearing aid is in the "off" position or the volume is at the minimum volume of "1", otherwise the instant sound will make you feel uncomfortable)