[dedward]

Very difficult to do - the induction element won't start until a significant (pan-sized) amount of ferrous material is very close to the cooktop, and shuts off the moment it's lifted away - there isn't enough room to get your wrist in there - and it's doubtful that your watch by itself, even if it was made of iron, would be enough to trigger the sensors on the element and let the element turn on..

Safety features and all that - they thought of that already.

Rings, watches - all safe.