Scan to find any phones devices with wifi on

I am working in a testing lab where people take tests. The director that runs it wants me to be able to scan and see if anyone taking a test has their phones wifi turned on (they are not allowed to access the internet during the tests).

I have been researching nmcli dev wifi and iw dev (cardname) scan and am getting inconsistent results.

Can anyone point me in a better direction to see (not connect to) any phone wifi that is turned on?