Casio G-SHOCK GW-M5610 (module 3159) with gesture controlled light switch - where we are going, we don't need hands [using motion sensors for sensible application for one handed users]
A solar powered radio controlled wrist watch with gesture controlled light switch rocks. Where we are going, we don't need hands ; ) one hand might be perfectly enough.
With one hand but not two, wrist watches are an issue or a subject.
Since over 10 years, I am a huge fan of Casio's solar powered radio controlled watch series. Clearly, they are always running and always precise. However the Casio GW-M5610 model with radio control and solar power adds an extremely clever feature - motion or gesture switched backlight.