Run a custom function while the screen is off

I have been playing around with the use of Lua scripting to try and achieve a similar face to the apple watch fitness app. The idea is to notify you when you have been not moving for 60 min. To do this, I would need to store the last time that a step was recorded (or x steps in y minutes). But right now none of the functions work unless the screen is on, so you only can track steps taken while the screen is on. If we could monitor sensor data in the background like every minute or 5 minutes or have an on_change(sensor) function, that would be awesome For more info, see here: http://www.reddit.com/r/WatchMaker/comments/322mlk/spent_most_of_the_day_on_watchmaker_but_im_going/