OK so now we know how to lock down the box, and what the terms are. Now how do we make sure our security is working?

Wireless intrusions detection:
Even the best security can be cracked. So for further protection monitoring your network is generally a good idea. There are many free tools out there to help you with this. The tools use different methods to help you, so take a look at them and figure out which you would like to use.

Your Router-
Yes, you read that right; your router will be the first tool you can use. Many wireless routers allow you to see what IP addresses are leased out and to whom. If you are using static IP addresses then just only allow your addresses. And be sure to turn on logging, that way you can see who tries to connect.

AirSnare - http://home.comcast.net/~jay.deboer/airsnare/
AirSnare is a wireless intrusion detection program that will detect and notify you of unknown/unfriendly MAC addresses if and when they try to gain access to your network.

Ethereal - http://www.ethereal.com/
Ethereal is a network protocol analyzer (packet sniffer). It will let you monitor all traffic on your network, and includes a source and destination IP for all packets that are captured. With a few simple filters you can set it to not show traffic from known IP addresses (the ones you set on your computers) and anything unknown will show up.
Programs like Snort, Network Sniffer, and airsnort can accomplish this also

Angry IP scanner - http://www.angryziber.com/ipscan/
Angry IP scanner does just what its name says, it scans IP addresses. So set the range for your subnet, set the option to scan for open ports that probably will be open because any decent fire wall will block a ping. (I scan for ports 135, 139, 445, 5900, and 3389) Be sure to set it to continue scanning ports on “dead” machines, or else when the box doesn’t respond to ping it wont scan them. (This can also be done with Cain & Able, nmap, and any other IP scanner)