@cyberdyne I had the same idea two days ago and did some research on it. I also asked /r/smartmirrors for some advice on it and got pretty good tips. The bottom line is, if you want to have a solid, non hacky solution supporting both iOS/android go the other way round with the use of beacons.
@bez252 Actually what they describe might also work for you, based on a quick glance through the setup code.
To shutdown from the node_helper you need to change some code in the file(will be in MMM-Button/node_helper.js in your file system). Here is an example from my module to shut down the RPi, you can replace the self.sendSocketNotification(...) in the node_helper with a similar command:
exec('sudo shutdown -h now', null);
Also, at the beginning of the file you need to include the exec function, like here: