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.
This seems to be a known "issue":
From Apple support pages
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:
This can occur due to:
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.