The app I demonstrated in this video is a free application letting you to measure noises and sounds around you.
It uses built-in microphone or your device to measure sounds. SPL (Sound Pressure Level) Sound Meter comes with an elegant gauge view to show the exact level of sound in decibels. Graphic view is also available to visualize evolution of sounds around the time when you measure it. Application informs you about current noises to better understand what represents sounds you measure.
This app offers you a screen to calibrate the level of noises of your microphone because it depends also of your hardware specifications.
Note that most of microphones on devices are made to record human voices. So, maximum noises that can be measured are limited around 100 dB in some cases.