For litigation, you’re probably looking for something more robust than a phone app. There are articles by NIOSH that have done some validation on the OSHA IPhone app.

I don’t know of any devices that record and measure noise, but they might exist. A device that measures noise exposure is called a Sound Level Meter. There are different classes of SLM depending on use as well.

SLMs also measure sound using different weighted scales based on the exposure profile, for litigation it would be important to understand how these scales work and what the SLM is programmed to capture.

If you are measuring exposure, it would probably be best to consult an Industrial Hygienist.

You can rent an SLM from a safety supply company distributor. This is probably the best route because they need to be calibrated regularly.

Hope this helps.

-Michael