Need an watch with cellular capability first!
However, if I get the thrust of your interest, this is for tracking small kids for which its not very practical to have a smartphone on them at all times.
The main author of xdrip+ has also developed a DIY solution for that, called Parakeet, a small piece of hardware about the size of a pair of AAA batteries, that is dirt simple to build. Combines a microcontroller and cell module into a very small footprint that can easily be "attached" to a kid some way. This provides exactly what a parent of a young PWD is looking for -- uploads to Nightscout, provides real-time monitoring.
Here's the link to jamorham's diabetes project page. To a non-engineer, this stuff may look complicated -- it's really not. If anyone decides to give any of this a shot, see if you can find a friend in the area that has some DIY engineering background to help (we're everywhere), or, if you have ANY soldering skills AT ALL, dive right in and give it a shot. This is a really, really, easy one.