Muting should do this. It would mute any sound except media and alarms. Press and hold power, as if you were shutting down the device. It should bring up power off, reset, and have sound options across the bottom.
I seem to have turned notifications off and can't figure how to turn them on. I go to settings > sound > volumes and see that notifications has a slash through it. How do I turn it on? I'm using a DROID 4.
Problem solved. Somehow Ringtones got set to zero volume, which turned off Notifications. I dragged Ringtones to full volume and Notifications came along.