I can't offer the DIY BORG look - though it would be awesome! Neither can I offer anything as small as a watch. But, a black box the size of a pack of cards is typical.
Let's look at two Arduino applications:
1. The 24/7 monitoring of your tremor and speed of movement. The data is provided by an accelerometer, and stored on a micro-SD card.
2. An aid for better posture. The data is supplied by a magnetometer. A beep is sounded if you're slouched forward or leaning to the side.
The components for each of these tools can be bought for about £20.
I suspect that we will soon see hundreds of apps being available, from fall warning detectors to transcranial stimulators. The issue is how can we get these available as quickly as possible, at a price that is affordable by all PwP?