Intelligent Ringer is an application by developer "soulreaver1" that aims to fix this ever annoying problem. The app sets the volume of your ringer based on the ambient noise environment in which your smartphone is working. It can also detect whether or not the phone is in your pocket. Unlike other apps Intelligent Ringer adjust its internal settings to the particular device, which makes a world of difference on the measurement and settings process.
It does respect silent mode, so when the phone is in silent mode it will not auto adjust the ringer setting. The app also includes many settings so that you have full control over everything! Grab this App from the link below!
Via Play Store