Answer to: Where is the Reed Switch? | MacBook Won't Sleep When ClosedI had the same problem when I swapped screens between different models of 15 in unibody MBP. The earlier one (with the removable battery hatch) has the sensor on the right side of the keyboard. The newer one (mid 2009 with SD) has it on the left. You can easily find the magnets in the screen and tweak the sensor by sweeping a small magnet over them. You can also find magnets on top of the screen for holding it closed. I thought about putting a strong, small rare earth magnet on the outside of the screen with hot melt glue or such, but never did it. I got used to pressing the power button and then "s" to put it to sleep before shutting the lid.