Secure Your Wireless Network: Cast Out Wi-Fi Intruders

Are you the only one enjoying your home network? Here's how to detect trespassers and block them from sucking up your bandwidth.
We all love the convenience of our home Wi-Fi networks, though it's likely that we're not the only ones. If you haven't adequately secured your wireless, it's possible that others—your neighbors and various other passers-by, for example—are happily gobbling up the bandwidth you pay for. Now, to be honest, you're probably not using it all, and sharing is the neighborly thing to do. In fact, many routers will help you do just that (share, not be neighborly). Of course, it would be equally considerate if that guy down the hall offered you some cash to use your network.
That said, you may have some very good reasons for keeping your network locked. So, we've gathered some tips for finding out if someone is using your 802.11-based signals as their own, and how you can block them out.
(Note: Every model of wireless router has a different interface, even if they're from the same company. However, all have similar tools. I discuss them generically here, but if you poke around in the settings, you'll find what you need. Better yet, call the geekiest person you know to help you out. Mom, I don't mean me.)