So to start I wasn't quite sure about where this question should be asked, so feel fre to relocate it if you want.
I'm setting up a system to notify me when a user enters an area. My plan is to use an old PCIE WiFi card powered from a small battery to detect when its within range. I want to know if a powered WiFi card needs to be initialized by the CPU or if a 5v power buss would be to have it show up in something like airodump-ng.
Absolutely it needs to be configured by a host CPU. A WiFi card is a pretty dumb device - it's up to the host CPU to configure it in the right operational mode, often give it a MAC address, and of course to handle all the WEP/WPA and the entire 802.11 and TCP/IP stacks.