July 2022: This project is not ready for prime time.
Using motors to alert the user seems logical and straightforward, but every naive approach has had associated problems - problems we are solving, which require official research and experimentation.
Simply put, we've been busy experimenting with the basics to get good results to use as a basis for an acceptable solution.
There have been several other pager motor projects with this purpose, and these projects have essentially gone nowhere, so they may have encountered the same problems.
Right now we're looking into the level of resolution a human arm (and belly and calf) can reasonably detect. A straight line of 4 motors going up the forearm is difficult for a human to distinguish individual motors, but my colleague has suggested that the line could spiral up the arm - so that motor 1 is on the wrist top, motor 2 is on the side, motor 3 is on the bottom, motor 4 is on the other side, and so on.
That's is a really good idea. We now have the rapid demo tools to quickly set this up and try it.
We've also had a bunch of suggestions for interesting applications to the system. The dev team is still interested in pursuing the project, and we'll be making further developments over time.
Shout out to PCBWay for sponsoring the project - you guys rock!