Phase 1: the phone app

Here's my current rough plan for the phone app part of the project. It will consist of a service and various user interface modules. One of the UI modules will be the main app that displays the watch and allows the user to access settings. The service will enable other UI modules such as the homescreen widget and lockscreen widget. It will also provide notifications through the system notifications mechanism. The service will keep track of the user's movements, possibly importing historical movement data from Google Location History (if that has enough detail to be useful), and maintain a database of the user's travel time between different points on the map. It will also pull event data from the user's calendar and give that, along with its predictions of promptness, to the UI modules for them to display to the user.

However, at first, I will develop a single monolithic app as a prototype. Once that's working, I'll split the modules apart and, I suppose, provide an API. (I have no experience whatsoever with APIs, so I'm really not sure yet what I'm doing there.)

Phase 2: the hardware device

The hardware device will connect to the phone app using Bluetooth or Bluetooth Low Energy. It will use a Switec automotive instrumentation stepper motor to turn the needle to indicate the user's current promptness. It will have a small OLED or LCD screen in the bottom quadrant to display info about the upcoming event. It will also, of course, have a rechargeable battery and charging mechanism.

Phase 3+: more ways to reach people

I would like to expand to other devices in the future, such as smartwatches. People with smartwatches would probably prefer to use those over pulling out their phone (let alone a standalone pocketwatch); that's why they have them, after all. I'm also open to other ideas about where to go next.