Application "Sound Meter HQ Pro" uses built-in microphone to calculate sound level (noise level) of surrounding. Result of the measurements is displayed in decibels on the screen of you phone. DISCLAIMER: Don't treat this utility app as a professional device to measure decibels. This tool uses built-in microphone, which was designed to capture human's voice. Such microphone is not able to capture sounds above ~90 - 100 dB (Maximum value differs depending on kind of microphone you have). In addi