SmartSleep for Mac Notebooks

I’ve always loved the nearly-instantaneous sleep feature of Mac notebook computers. If I needed to get up and go with my 12″ Powerbook G4, I could snap the lid shut and throw it into my bag. Recently I grabbed a new Macbook Pro, and noticed that the computer didn’t go into sleep instantly. Instead, the computer was writing RAM to the hard drive, a process called hibernation, which kept the system’s state safe in the event of power failure (your battery dies, or you swap it out for a new one). This is a great feature, but I don’t have a secondary battery to swap, and I was getting tired of closing the lid and waiting for the white light to start pulsing. If you don’t wait for the light to pulse, then you’re moving the computer while the hard drive is active, and you risk damaging the drive. The sudden motion sensor (SMS) is active while the machine is in use, but apparently isn’t active during this hibernation process.

I can across this great blog post by David Alison describing the situation and showing a quick terminal command you can use to disable the hibernation mode. After running the command, shutting the lid on the notebook will skip dumping RAM to the hard drive, and will just instantly sleep. I was hessitant though, because if you don’t hibernate and your battery dies while the machine is asleep, you lose your system’s state. Also, if I bought a second battery, would I remember to hunt down the terminal command and reverse the setting? I’d also be losing the instant sleep state again.

Thankfully Jeremiah posted a link to SmartSleep in the comments of David’s blog. SmartSleep is a preference pane that lets you turn on and off hibernation (writing RAM to disk) with a drop down menu. It also features a mode called SmartSleep, where the computer will hibernate if the battery is below a certain threshold of charge, but otherwise sleep will be instant. Perfect!

If you’re a Macbook user and you want instant sleep, grab a copy of SmartSleep for yourself.

Chris Owens


  1. thanks for this. i’ll be bookmarking it for when i upgrade from a powerbook to a mbp at the end of december.

  2. In SmartSleep mode, if I put the computer to sleep when the battery is above the threshhold, and as the computer sleeps the battery runs below the threshold, will the computer eventually hibernate or will the battery just run out and cause a power loss?

  3. Alan,

    You’re right. The threshold can only be measured before you close the lid to sleep the computer. Since this is a software tweak, it can’t do anything while the machine is asleep.

    The RAM doesn’t use a ton of power, and the machine should be safe in sleep mode for a day or two I’m sure.

    I have mine set to turn on hibernation mode at 20% battery, hoping that is conservative enough to save me if my battery is going to die.

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