kismet

An 802.11 Wireless Network Sniffer

Kismet is an 802.11 wireless network sniffer. This is different from a normal network sniffer (such as Ethereal or tcpdump) because it separates and identifies different wireless networks in the area. Kismet works with any 802.11b wireless card that is capable of reporting raw packets (rfmon support), which include any Prism2-based cards (Linksys, D-Link, Rangelan, and more), Cisco Aironet cards, and Orinoco-based cards. Kismet also supports the WSP100 802.11b remote sensor by Network Chemistry and is able to monitor 802.11a networks with cards that use the ar5k chipset.