MacBook and MacBook Pro: Some computers may unexpectedly go to sleep when stacked for MacBook and MacBook Pro

If you stack certain MacBook or MacBook Pro computers on top of each other, one or more of the stacked computers may go to sleep unexpectedly.

Depending on when this happens it may appear that the computer is having difficulties starting up. Stacking the computers can result in the top computer going to sleep before it’s completely started up.

Resolution
Do not stack the computers.

When stacked, the magnet in the bottom computer may activate the magnetic switch in the top computer. This is normal behavior. Automatic sleep operation works based on magnets; a switch in the MacBook Pro, known as a Hall Effect switch, is activated when the magnet in the display clamshell gets close to it. This is how your computer knows to go to sleep when you close the display.