Sound Meter is a free Android app developed by SO LAB that allows you to measure the decibel values of environmental noise. It is a useful tool to perform a sound test or noise measurement, as it displays the dB values in various forms. The app requires permission to access the microphone or mic to detect sound.

The app offers different graph meter and digital views to display the current noise dB value. The gauge or meter indicates the decibel level of noise, and the real-time update on the chart graph is an added advantage. Sound Meter also allows you to calibrate the decibel for each device, and display the min/avg/max decibel values.

However, it is important to note that the decibel meter or soundmeter might not be as precise as an actual Sound Pressure Level Meter(SPL Meter), due to most device's microphones being aligned to the human voice. Also, the maximum values are limited by the device, and very loud sounds (over ~90 dB) may not be recognized in most devices.

Overall, Sound Meter is a useful app to measure environmental noise and sound using your smartphone, but if you need more accurate dB values, we recommend an actual sound level meter.