This item can be used for sound amplifier. When you see film / watch movie, enjoy the drama / watch the play, attend meeting, or have classes, the product can help you to hear the sound clearly and . While in forest, if you want to hear very slight sound, a . Features - - Material: ABS - Size: 9x6x4cm - Mini Output: &ge;110 &plusmn; - : &ge;30 &plusmn; - Frequency Range: 300~4000Hz - Input Noise: <=40 - Battery: (included) - Working Voltage: .5V - Working : <=3mA - and 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 . Package list: 1 x K-188 3 x Earplug (different sizes) 2 x 1 x User manual 1 1 x tool