Noise monitoring

Hi everyone,
I would like to develop an application to monitor the sound coming from the mobile phone microphone and if it exceeds a certain threshold display an alert.
I searched the palette for components that might be useful, but couldn't find an instrument that monitors the sound coming from the microphone.
The only tool that comes close to my purpose is SoundRecorder, but I don't know how to see the detected value of sound / noise.
Can anyone help me? Many thanks in advance

How about this extension (you may need to scroll down a little to "Sound Analysis")

http://appinventor.mit.edu/extensions/