The Red "18" line is not a "function" block per se, but a path indicator (essentially identifying the power routing). So, unfortunately, that doesn't tell us whether there is a "master power switch" or not on the device.
If we're lucky, though, the Tricorder may be like the Communicator, in that - to be activated - you have open the device and hold down one of the "Buttons" (which, on the Tricorder, would be in #4 Block in the Hood) in order for that button to turn on the power and thus activate all of the functions. Thereafter, the magnets would serve the listed function - until the same button was again held down in order to turn the power off - also like the Communicator. That way, similar to the Communicator, you could display it in the Open position without a power drain.
The lack of specificity about alternatives to the magnets, along with a couple pictures we've seen so far, just had me concerned.
I was really hoping we'd get *more* information than they judiciously doled out to us this time around. But if this, and the next, Update (which they say will address "Making the things that will make the things" ie the "Cutting tools" etc) are any indication, it appears that - after whetting our appetites with information *dumps* in the first Updates - they're now going to stretch out what little information they feed us in the future - presumably in order to fill the MANY months it is apparently going to take to get the Tricorder into manufacturing, let alone distribution.
The only *truly* new information that we got here was:
The ARM processor is a Cortex-M7.
The screen is 320x240 LCD.
There will be "archive files and interesting pieces of pre-recorded information" in the memory [SDRAM and Flash].
Two magnets will control "wake up" and 'sleep' functions.
An Optical sensor will detect the difference between the eight different data discs when each is loaded next to it - the choice of which will determine which data and sensors can be used at a given moment.
I for one am looking forward to reading about how they cut the tooling for the tricorder injection molding process. I assume they used a similar process to how they created the texture on the communicator. As replica makers go, they've really set a high bar.