You&#x27;re falling victim to the same trap as what Snowden is talking about.<p>Serial numbers on bills are routinely scanned and tracked. There&#x27;s a discussion here:<p><a href="https:&#x2F;&#x2F;www.reddit.com&#x2F;r&#x2F;explainlikeimfive&#x2F;comments&#x2F;3ou4h4&#x2F;eli5_how_are_the_serial_numbers_on_banknotes&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.reddit.com&#x2F;r&#x2F;explainlikeimfive&#x2F;comments&#x2F;3ou4h4&#x2F;e...</a><p>It&#x27;s not done at the point of sale. It&#x27;s done when the money is returned to the banks themselves, and when they&#x27;re dispensed at ATMs. Cash doesn&#x27;t circulate for long and anti-money laundering laws prevent payment for many expensive items in cash, so this can provide important clues about where the money goes.<p>For instance, withdraw money from an ATM, pay for food at your local grocery shop, and the bank&#x2F;govt can see &quot;withdrawal from account Herr Schmidt at 7:03pm Thursday, deposited by a grocery store down the road the next day&quot; and conclude the money was used to buy food ... or at least had at most one hop in between.