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 loudly. While in forest, if you want to hear very slight sound, it will be a good choice. Features – Material: ABS. – Size: 2.5x2x1.5cm. – Maximum saturation sound pressure: 129dB ± 4dB – Maximum file acoustic gain: 48dB ± 5dB – Harmonic distortion: = 18% (450 = F = 5000) – Frequency response: 450-3500Hz – Equivalent input noise: = 30dB – Battery type: AG3 button cell – Operating voltage: 0.2 ± 0.1V – Operating current: = 4mA – Suitable for severe hearing loss people. – Smaller than a credit card, discreet enough to fit easily in your pocket or handbag.