Sound Level Meter is in the 4th set of the Smart Tools collection (noise, decibel meter). REMEMBER. The built-in microphones were aligned to human voice (300-3400Hz, 40-60dB). Therefore the maximum values are LIMITED by the hardware limitation, and very loud sound (100+ db) cannot be recognized. Moto Droid (max. 100), Galaxy S3 (81dB), Galaxy Note (91dB), Galaxy S2 (98dB). SPL (sound pressure level) meter app uses your built-in microphone to measure noise volume in decibels (db), and shows a reference. We had calibrated many android devices with the actual sound level meter with dB (A). See the 6-7th pictures. I had calibrated many android devices with an actual sound level meter. You can trust the result in routine-noise levels (40-70dB). But, please use it as an auxiliary tool. Pro version added Features :- Sound Meter and Vibrometer are integrated- Statistic menu with saving log data- CSV file exporting- Level notification- Line-chart duration- More models are calibrated- No ads. Do you want more tools? Get [Sound Meter Pro] and [Smart Tools] package. For more information, see the manual, Youtube video and the blog. Thank you.