Bucky's is a sensor, a battery and a... [he pauses momentarily, thinking of the right word] ... a very tiny radio. It'll be sending a signal to your bracelet.

[he pokes at the screen and enlarges the second bracelet]

Yours is simpler. It receives the signal, if the signal stops it starts beeping.

[swipes at the screen so all the parts come apart]

I could make them more complicated. I was, actually, but then I realized I could do this instead. Finish them more quickly.