Via the register
“US peripherals maker Kensington has introduced worlds first: a detector that will locate Wi-Fi networks. The small device detects 802.11b and 802.11g signals from up to 200 feet away and filters out other wireless signals, including cordless phones, microwave ovens and Bluetooth networks. Three lights indicate signal strength. For $29.95 that’s seems a bargain.
However, there is no display information on the owner of the network or whether the hotspot is commercial, free or private; nor is there any information about the level of security provided (WEP or WPA, for example).”