AirSnare

AirSnare is a witty application that can monitor your wireless connection in order to detect intruders and to notify you accordingly. It identifies the MAC addresses that are trying to connect to your network and allows you to track them back to their IP address.
AirSnare keeps untrusted users off of your wireless network and to this purpose, it delivers an intrusion detection system that will keep you alerted of such attempts. It manages to do so by continuously monitoring network traffic for unfriendly MAC addresses.
In order to enjoy these perks, first you need to accommodate it on the system, provided that you are equipped with a 802.11b wireless card and several third-party components such as WinPcap and Ethereal, which are also bundled in the installer.
AirSnare automatically detects your network adapters and lists them, so you can select the ones to be monitored. However, prior to this, it is recommended that you define the list of friendly MAC addresses, belonging to the devices that you trust to connect to your wireless network (printers, routers, laptops, etc).
Assuming that the list of friendly MAC addresses is complete, you are ready to start the monitoring process. Any intrusion is signaled via a red screen and an alarm sound, with the possibility to trace that connection back to its original IP address and ports, so you can found out who exactly is trying to use your wireless setup.
You can also configure the application to send emails to the administrator in case intrusions are detected or to send a message to the computer that’s trying to connect, in an attempt to inform them of their inappropriate behavior.
AirSnare makes quite the detective, considering all of the above. It is a decent network traffic monitoring suite, with alert settings and email notifications that keep you up to date with unwelcomed intruders.