[throw3849]

WiFi on phone sends periodic pings to discover new access points. MAC is unique...

[goatsi]

That hasn't been true for years, both Apple and Android devices now use a random MAC for probing pings.

https://support.apple.com/en-ca/guide/security/secb9cb3140c/...

https://source.android.com/devices/tech/connect/wifi-mac-ran...

[fsflover]

Librem 5 smartphone has hardware kill switches for WiFi/Bluetooth and cellular modem.