My Mid 2012 Macbook Pro Goes to Sleep when I put my iPhone on the Left corner, Is there any way to prevent this ? it doesn't do it every time, but it can get extremely annoying when it does
They use a magnet to sense when the lid is closed so the display will shut off. The phone has a magnet in there and when the phone is placed on that corner, the MBP thinks you have closed the lid so they display turns off and the computer sleeps. I've done the same thing with my 2015 MBP.
It's a known issue. On the 2011 MBP 17" the sensor's on the lower right, so I've learned to place the phone on the left when carrying both. My iPhone SE has the vibrator motor (with magnets) near the bottom, which is typical.
Right-- it's probably the speaker magnet causing it since it's strong enough to hold a paperclip to the back. I suppose Apple could fix this by making their sensor less sensitive (the lid magnets are much stronger), but that would likely cause other problems.