Features:
Sound amplifier behind the ear 
Super mini size and light weight, not easily to be seen 
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 

Specifications:
Max Saturated Sound Pressure: 130dB+5dB 
Sound gain: ≥ 50db
Harmonic Wave Distortion:≤ 5% 
Frequency response Range: 300--- 4000 Hz 
Input Noise: ≤ 30 dB 
Power Voltage :1.5 V 
Working Current : ≤4mA 
Battery Type: AG13 button cell battery (included)