How to put Wifi card in monitor mode? When I run tcpdump, I do so after having connected to an access point.
Is there a way to run tcpdump without having connected already?
Use tcpdump -I. -I will put the chosen interface into monitor mode, and doesn't need to be connected to an access point.

The full command would be (if your Wi-Fi interface is en0):

sudo tcpdump -Ii en0