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Retailers are replacing price stickers in aisles with electronic shelf labels. The labels prices can change as often as every 10 seconds. Hot outside? They can raise the price of water & ice cream.

https://www.npr.org/2024/06/17/nx-s1-5009271/electronic-shelf-labels-prices-walmart-grocery-store

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I don't know the current status on this, but it worked by recording your phone's mac address (or bluetooth address) when your phone scans for wifi networks. So it could track you without you even needing to join the network. AFAIK this particular tactic was countered by Android and IOS randomizing the mac address it sends out (your networking stack can simply lie about it).