I was surprised to learn that some wireless cards that work perfectly fine for general networking, won't work with Kismet or Airsnort. It turns out that in order for a wireless card to be used by either of these two programs, the driver for the card needs to support monitor mode. If monitor mode is not supported, then you won't be able to use programs such as kismet or airsnort

The easiest way to tell if your wireless card supports monitor mode is by attempting to put it into monitor mode using the iwconfig command. The following shows the expected output:

[root@probe root]# iwconfig eth1 | grep Mode
          Mode:Managed  Frequency:2.437GHz  Access Point: 00:00:00:00:00:00
[root@probe root]# iwconfig eth1 mode monitor
[root@probe root]# iwconfig eth1 | grep Mode
          Mode:Monitor  Frequency:2.437GHz  Access Point: 00:00:00:00:00:00
[root@probe root]#