Wall-penetrating radar is already a thing: https://www.youtube.com/watch?v=w4eret12KN0 https://www.youtube.com/watch?v=w4eret12KN0 Probably a lot more accurat

Wall-penetrating radar is already a thing: https://www.youtube.com/watch?v=w4eret12KN0 https://www.youtube.com/watch?v=w4eret12KN0 Probably a lot more accurate than (ab)using wifi routers for the purpose, but the benefit of WiFi is that other people have already conveniently installed the hardware inside their homes.