Chosen Solution
On my 2015 MacBook Pro I could put the laptop display to sleep using a small, weak magnet on the left side of the case. I did this to use my external display as the only monitor. I’m not sure if this still works on the 2016 with Touch Bar.
Here’s the location of the Hall sensor:
Apple uses strong neodymium magnets, however, with your Mac booted .. even to the login screen … move the magnet (on a piece of paper towel so you don’t scratch the surface) around the outer top of the Top Case until you find the sensor location (i.e. until it goes to sleep) … it will work.
On my MacBook Pro (15-inch, 2017), I needed two magnets - one on each side - to make it think the lid was closed. I was able to do this by placing the magnets on the speaker grilles on each side, a little way down from the thunderbolt ports. It seems likely they have added a second sensor to avoid the computer suspending by accident if you move a magnetic object close to it.
