Editor's note: This app is no longer being developed or supported by the original developer.
If you've never heard of it before, you might be wondering what "safe sleep" is (but if you have heard of it, you can skip the next couple paragraphs). When the battery on one of Apple's notebook computers (including the MacBook, MacBook Air, MacBook Pro, and some late-model PowerBooks) is very low, OS X will put the machine into what Apple calls "safe sleep" mode. This is similar to standard sleep, except the contents of the RAM are completely written to the hard drive and all power shuts down. You can even remove the battery while the machine is in safe sleep. To wake the computer from safe sleep, press the power button on the computer. A progress bar will display (startup will be noticeably slower than a normal wake from sleep), then your computer will be restored to how it was before safe sleep was invoked.
This feature is called "hibernation" in the Windows world, and it's one of the very few features I missed when I switched from Windows to Mac. (The other big one was how Windows deals with moving files, which can be replicated on the Mac side using moveAddict.) One of the nice things that Windows computers have is the ability to choose to hibernate when you are shutting down the machine. For years, I never turned my Windows laptop off; I only hibernated. Unfortunately, Apple has not made that feature available to Mac users.
That's where SafeSleep.app comes in. When you launch the app, it displays several options. The one I'm most excited about is "Safe Sleep Now," which lets me choose safe sleep without having to change the way the Mac usually works. I can still just close the lid for normal sleep (or choose it from the window above), but if I want to make sure to trigger safe sleep, it's now much easier to do.
"Always use Safe Sleep" will tell the computer to never use the normal, faster sleep mode. If you choose that and want to change it back later, select "Only Safe Sleep in Emergencies." You can also totally disable safe sleep; this isn't recommended for obvious reasons, but if you're willing to take the risk, disabling it can make the process of putting your Mac into "normal sleep" faster.
Although safe sleep was designed for portable Macs, you can also use it on desktop Macs. At night, I use safe sleep on my iMac because, otherwise, it seems to wake from "normal sleep" on its own. A word of caution, however: be sure to unmount any external drives that are connected to your Mac before entering safe sleep. Even if they remain physically attached to the Mac, OS X thinks that the disk was ejected without being unmounted, which is something you want to avoid. Physically connected drives will automatically be remounted when the machine wakes from safe sleep.
SafeSleep is free and can be downloaded from MacUpdate.
Apple MacBook Air 13-inch (early 2015)
Apple MacBook Pro 15-inch with Retina Display (mid 2014)
Apple OS X Yosemite