NIOSH Sound Level Meter 4+

This award-winning app combines the best features of professional sound level meters and noise dosimeters into a simple, easy-to-use package.
- Developed by experienced acoustics engineers and hearing loss experts.
- Completely FREE – No ads, no limited features, and no in-app purchases.
- Tested and validated (accuracy ± 2 dBA) according to standards in a reverberant chamber at NIOSH acoustics lab – the only proper method to validate accuracy.
- Trusted source and world-class expertise in noise and hearing research.
- Meets Type 2 requirements of IEC 61672:3 SLM standard when used w/ external microphone.*
- Provides the most relevant metrics found in professional sound instruments today. Averages such as LAeq and TWA, Max and Peak Levels, Noise Dose and Projected Dose according to NIOSH and OSHA standards, and all three major weighting networks (A, C, and Z).
- Capability to calibrate either internal or external microphone. Reporting and Sharing data.
- Up-to-date informational screens on what noises are considered hazardous, how to conduct a noise measurement, how to properly select a hearing protector, and guidelines for preventing hearing loss, all at the palm of your hand.
- Excellent and timely support from NIOSH hearing experts.
- Support for Apple's Health (Hearing) app.

* Celestina M, Hrovat J, Kardous CA [2018]. Smartphone-based sound level measurement apps: Evaluation of compliance with international sound level meter standards. Applied Acoustics, 139:119-128. https://doi.org/10.1016/j.apacoust.2018.04.011

More resources (including instructional videos and a user manual), a science blog, FAQ, and information about how to interpret results can be found on the NIOSH SLM website https://www.cdc.gov/niosh/topics/noise/app.html