The Sapienza computer scientists say Wi-Fi signals offer superior surveillance potential compared to cameras because they’re not affected by light conditions, can penetrate walls and other obstacles, and they’re more privacy-preserving than visual images.
[…] The Rome-based researchers who proposed WhoFi claim their technique makes accurate matches on the public NTU-Fi dataset up to 95.5 percent of the time when the deep neural network uses the transformer encoding architecture.
First of all: cardboard does NOT block electromagnetic waves. You need a Faraday Cage for that. And even then, it has to have holes of a certain size to block specific wavelengths/frequencies. It’s why you have a mesh on the door of your microwave for example.
Secondly: they’re not attempting to photograph you. Just identifying your unique signature once would allow them to track your location anywhere where they have the gear installed.