How to get the decibel level of a mobile micro (Android/iOS)

I want to get the accurate decibel level at a T time, test it and if it's loud enough in comparison to the usual background sound, do an action like, in my case, start the recording of a video.

I have the recording video code, but I can't find how to get the decibel level of the mobile micro (I don't want to record sound, just test it maybe every frame if it works, something like that..)

Thanks for help :D !