As it turned out, it does not function through tattoos. I have a tattoo on my wrist, and as a result, not a single sensor functions; they vibrate when walking but not when calling or sending messages (where is the logic in that?). Nobody, not even the office sellers, is aware that they don't operate through tattoos. stores Apple Watch, Xiaomi Mi Band 3 or 4, and some Samsung (I just tried one in the shop) all have sensors that function through tattoos.
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