I recently acquired a GPS-capable watch. Along with other bells and whistles it is ANT+ capable. ANT+ is a low-power wireless protocol similar to Bluetooth, but designed for remote sensing and control. Since GPS watches are almost entirely dedicated to running, cycling and other "fitness" applications, the only compatible products are things like heart rate monitors or "foot pods" that count your steps. The only thing you can control is an "action cam" that you stick on your helmet while cycling. The ANT+ community has only one thing on its mind. Apparently a bunch of engineers who happen to be jocks.
How about an ANT+ interface to the X10 system to work with these watches? Perhaps monitors that set off an alarm on your watch when the basement floods, or someone comes in the driveway. Push a button on your watch to turn the outside lights on or off when you're sitting n the deck. Push a button to send the proverbial "I've fallen and I can't get up" message. Read the temperature of your outdoor thermometer, or even your meat thermometer.