Yes, I understand your concerns. Sure thing, prior to "shaking" operations the navigator must be brought into the "operations" mode. Is the regular "Power" button is too awkward to use? Both of mine are superb. I like the "dangling" command idea. The screen off mode trigger could be configured simply for a certain device orientation (like the vertical one, on the lanyard). I can rig an app for proof of concept testing soon, however at the moment I'm working with the Google Maps API, which might be not good for a serious testing in the field, as it requires an Internet connection (no caching is possible with their API). However, I plan to switch to the OSM at some point, as it looks robust enough already, with many hiking trails mapped by the community. I doubt I'm going to compete with the plethora of Android NAV aps, but the OSM community may listen to this idea and add such a feature to my favorite OSMAnd project, for example.

By the way, when hiking I'm carrying my smartphone on the neck as well (not sure what you mean about the shoulder though, under the armpit probably?). The lanyard is long enough to operate the device, as well as to put it into the shirt's front pocket, when dangling is inconvenient (i.e. when climbing a rock), or a bit more protection required (i.e. dust).

Also I have invented another technique for the convenient phone lanyard, which does not require a loop, thus not require a breakout device for it either. With that, the phone is riding high (just below the shoulder line) on the one side of the chest (pectoral), the lanyard goes up over the shoulder, behind the neck, over the other shoulder and the other side of the chest, and connects to the shirt's button hole or to the collar of the T-shirt (with a pin/clamp/-binner). That position is much more safe and convenient for carrying the phone ready for action, as it's not actually "dangling" much when your torso moves. You can easily glance at the chest's side to see some info quickly, or pulling the screen a bit, as well as operate it to some extent, and you can always move it over the neck and bring in front of you for more extensive operation. It's is still short enough to stop the phone's falling from your hands far from the ground. In fact, my phone's lanyard is a 5 "strands" folding transformer with an S-binner and a ring, which allows the neck, wrist, shoulder, belt, and even single finger carrying/holding I should make a post about it some day.