Sound Level Meter is in the 4th set of the Smart Tools collection (noise).SPL(sound pressure level) meter app uses your phone mic 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).REMEMBER!! The smart phone microphones were aligned to human voice (300-3400Hz, 40-60dB). Therefore the maximum values are LIMITED by the manufacturers. The very loud sound(100+db) cannot be recognized. Moto Droid(max.100), Galaxy S3(81dB), Galaxy Note(91dB), Galaxy S2(98dB)…See the 4-5nd pictures. Many devices had been calibrated by the real sound level meter with dB(A).* Pro version added Features:- Sound Meter and Vibrometer are integrated- Statistic menu and Save log data- 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.** Not compatible with: Xperia(X8, X10 mini), LG(Optimus One, P350), GT-I9001, ZTE, etc