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I have a MacBook Pro 13" with Mountain Lion and sometimes when I place my phone on the computer (usually on the left of the trackpad) the computer goes to sleep with no reason. Although this does not occurs systematically every time. Why that happens? Is it because some electromagnetic radiation from the phone influencing some parts of the computer? Couldn't think something else more logical.

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This seems to be a known "issue":

From Apple support pages

Mac notebooks: Magnets in devices may cause computer to sleep unexpectedly


Placing a device that contains a magnet (such as an iPhone) under your computer or on its palm rests can cause the computer to sleep unexpectedly. This can also appear to cause the computer to have difficulties starting up.

Resolution Computers that may have this behavior include:

  • MacBook (Late 2009 and later)
  • MacBook Air (2008 and later)
  • MacBook (13-inch, Aluminum, Late 2008)
  • MacBook pro (15-inch, late 2008 and later)
  • MacBook pro (17-inch, late 2008 and later)
  • MacBook Pro (Retina models)

This can occur due to:

  • Stacking computers. This can result in the top computer going to sleep before it's completely started up. For best results, do not stack computers.
  • Placing an iPhone or another magnetic device on top of a computer's palm rest. For best results, do not place devices with magnets on your computer. -Placing an iPad on the computer's palm rest since certain iPad cases also contain magnets.

This is expected behavior. Automatic sleep operation depends on magnets. A switch in the MacBook Pro body, known as a Hall Effect switch, is normally activated when a magnet in the display gets close to it when you close the computer. When stacked, the magnet in the bottom computer may activate the magnetic switch in the top computer. Likewise, the speakers in an iPhone contain magnets which can trigger the sleep function.

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