Sound Meter Pro is the 4th set of Smart Tools collection (noise, vibration, seismometer). SPL (sound pressure level) meter app uses your microphone to measure noise volume in decibels (db), and shows a reference. We had calibrated a lot of android devices using an actual sound meter with dB (A). REMEMBER. Most smart phone microphones were aligned to human voice (300-3400Hz, 40-60dB). Therefore maximum value is LIMITED by manufacturers, and very loud sound (100+ dB) cannot be recognized. Moto G3 (max. 80), Galaxy S6 (85dB), Nexus 5 (82dB), HTC Desire (82dB). Vibrometer app uses your acceleration sensors to measure vibration or the earthquake, and it shows a reference as a seism detector. The measured values are related to Modified Mercalli Intensity scale (MMI). If it is inaccurate, you can calibrate it so that maximum value is about 10-11. Pro version added Features:- No ads- Sound Meter and Vibrometer are integrated- Statistic menu with saving log data- CSV file exporting- Line-chart duration. Do you want more tools? Get [Smart Tools] package. For more information, watch YouTube and visit the blog. Thank you. Not Compatible with : Xperia (X10 mini), LG (Optimus One, P350), GT-I9001, ZTE, etc. No internet support : You can open this app without any connection. After installation, open the app 2-3 times with your device connect to WI-FI or 3G/4G.