Designed for those who are hard of hearing, using the LED flash on your iPhone is also handy if you simply don’t want to hear your phone ring or buzz every time you get a new message or call.
Go to Settings -> General -> Accessibility, and scroll down to “LED Flash for Alerts" and flip the toggle to the “on” position. It’s almost startling how bright the flash is. However, you’ll have to remember to rest your phone face down.
More: 25 Best iPhone Apps