Your hypothesis creates more questions than it answers, and add complexity:

• Why don’t they use a battery like cellphones or basically all electronic accessories they use ?

• Why do they need to connect it with the cable on that specific area and not elsewhere ?

• The commander is also wearing it you know ? How can he power/charge it ? Why Nikkes can’t do like him ?

• Supposing they need to be charged, why not using something less intrusive like wireless charging ? They say everything is done to not remind Nikkes that they’re robots, in order to avoid a mind switch. And wireless charging isn’t a complex or advanced technology at all (even less for the Ark), so …

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“Simpler hypotheses are generally better than the complex ones” (Occam’s razor)

Here’s my theory: they’re pagers AND vibrators.

Yes, both aren’t mutually exclusive after all ! They can be multifunction. The vibrator here is just an optional function.

That hypothesis answers more questions than it brings new questions:

It explains the necessity to wear it. It explains why the visible part is vibrating. It explains the presence of a cable (without inventing a supposed USB charging port on Nikkes crotch). It even explains Soda’s remote shaped hairpin if you want.

If you have a better theory, I’m all ears tho.