i found an app that says it will do it but u need to be rooted and i am not sure it works with the s3. You would need to try it and see.

https://play.google.com/store/apps/details?id=eu.chainfire.nomoarpowah&hl=en

 

Hello and welcome to the forum Stephanie.

There is also the option in settings of using blocking mode so that no calls or notifications will get through during a specified time.

 

What I like to do is to turn off notifications sounds while I sleep, so that an email does not wake me. I still take phone calls and have my alarm on. I use Volume Widget and turn off my notification sounds only while I sleep and then I turn them on when I wake up. You have to manually do this. You can configure a sound profile to turn off your ringer and notifications while leaving the alarm sound on. Just manually activate this profile before you go to bed and when you wake up, revert to your normal daytime sound profile.

 

many AOSP ROMs allow quiet mode, but those require root

 

I just put my phone on mute before bed, the alarm still works just fine.

 

I will repeat what has already been said: Blocking Mode - provides exactly what you are looking for.

 

I leave my phone plugged in, turn all the sounds down, and the alarm will still go off.