I love the Do Not Disturb feature of iOS. It automatically turns on at 10:30 PM and off at 7:30 AM on all of my devices - iPhone, iPad, and Mac. Only those on my Favorites list can disturb my slumber with a phone call. Until iOS 10. You can now let messages from certain people override Do Not Disturb and make an audible/physical alert. To do this the person must be saved as a Contact. Go into edit mode of the Contact and select the text tone. You'll now see a new Emergency Bypass feature at the very top of the screen. Flip the switch for those special people you just can't miss a message from.
ProTip: This feature could also be handy if you get alerts from Security Systems or other important places via SMS/iMessage.