OS X includes a number of built-in alert sounds—you can choose which one you’d like to use as your alert sound on the Sound Effects tab of the Sounds System Preferences panel. Today, though, I’ll show you two different things you can do with alert sounds—how to add additional sounds and how to create a “visual alert,” i.e. a screen flash instead of an actual sound.
First, to use your own sound effects as alert sounds, create a folder named Sounds in your user’s Library folder. Now just drop any sound you’d like to use into that folder—they must be in AIFF format, and you’ll want to keep them short. You can search the net for free alert sounds already in AIFF format, or you can convert your own using a tool such as Apple’s $29.95 QuickTime Pro or iTunes or one of many other such apps. Once you have a sound snippet in AIFF format, just move it into the Sounds folder you created earlier. Launch System Preferences, switch to the Sounds section, and on the Sound Effects tab, you should see your newly-installed custom sound. Select it, and it will become your new alert sound.
As an alternative to the aural alert sound, you might want to consider a visual alert—a screen flash. You can see how this looks by going to the Universal Access System Preferences panel, selecting the Hearing tab, and then clicking on the Flash Screen button. You can also enable screen flash here, by checking the box above the Flash Screen button. However, unless you mute your audio, you’ll also hear whatever alert sound you’ve selected. So how can you have the best of both worlds—a screen flash alert without having to mute your audio?
It turns out that the Sound System Preferences panel doesn’t like it if you tell it to use an invalid sound file. And it lets you know its displeasure by… you guessed it… flashing the screen! So all you need to do is create an invalid sound file, which you can easily do in Text Edit. Open a new blank document, type a space, and save it as Screen Flash.aif, or whatever name you want—just make sure you end it in .aif. Text Edit will then warn you that you’re using a non-standard extension; just go ahead and click the Use .aif button at that point. Save it into the Sounds folder you created earlier to hold your custom sound, launch System Preferences, and go back to the Sound panel.
On the Sound Effects tab, you should see your Screen Flash “sound.” Select it, and watch your screen flash. From now on, any system alerts should result in a screen flash, which will definitely get your attention without making a single sound.