Features Brand new and high quality invisible hearing aid sound amplifier Super mini size and light weight, not easily to be seen Adjust volume to the minimum before wearing Increase volume gradually to avoid sudden increase in sound Convenient for watching movie, enjoying the drama, attending meeting, or having class, it could help you hear the sound clearly and loudly Specification: Mini Hearing aid Max Sound Output: 110 dB ± 5dB Max Sound Gain: 30 dB ± 5dB Frequency Range: 300 4000Hz Input Noise: 40 dB Battery: A10 Button battery (included) Working Voltage: dc1.5V Working Current: 3mA Color: As the picture shows Package included: 1 x K-188 Hearing aid 3 x Earplug (different sizes) 2 x A10 Button battery 1 x User manual 1 x Box 1 x tool About Whistle , you can do this 3 steps to remove it. 1. Choose a suitable earplug to make the product sealed in the ear canal 2. Low down the sound volume 3. When you put into battery , please be quick , to put the product into the ear 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. Keep the ear plug clean Remove the battery if you don't use it for long time.