Pomcast.biz has introduced Disk Alarm (http://diskalarm.com), its first Mac OS X app. It requires Mac OS X 10.6.6 or higher and is available for US$3.99 at the Mac App Store in the Utilities category.
Disk Alarm will let you know in advance how much free space is available for your Mac to run smoothly. The app optionally alerts you when you have reach a certain amount of disk space with a sound. Disk Alarm can run in your menu bar for fast access to available free space and more.
You can check your disk space manually if you don’t want to have the software do it automatically. Disk Alarm offers the ability to see set the checked space in percents instead of MB/GB.