just because it isnt conneted to your network dosent mean it isnt sending data over side channels it could:
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use alternative networks provided by other devices (ring cams, amazon echo etc)
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decentral networks like apple or google tracking networks via phones
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it could strait out have a sim card with modem
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sending ultrasonic tones recived by ad tracking networks on smartphones
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high speed IR flickers that could be recived by smartphones distance sensor
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samsung service personal in the building across the street with a big telescope