As Jeff Gamet discussed in a previous article, you can turn on a setting under iOS that’ll flash the camera LED when an alert comes in. There’s a way you can do this on your Mac, too, and it’s useful if you have trouble hearing or if you just keep your devices muted much of the time. This option is available under System Preferences > Accessibility > Audio.
Press that “Test Screen Flash” button to see what it’ll look like, but after you toggle on the “Flash the screen when an alert sound occurs” checkbox, that’s what’ll happen from then on. So whenever your Mac needs to let you know something’s going on, you’ll see a visual cue along with the audio one. Neat-o!