WiFi Locator
There are all sorts of these things out there on the market – I saw an ad for the Hawking HWL1 802.11b/g WiFi Locator… and it looked interesting (directional)… I’ve seen mixed reviews, but some might find it good/useful. I know, I know…. “why buy a wifi locator when you could pull out a laptop/pda”…. part of it is probably because you DON’T want to drag out a laptop, part of it is looking for a device that will give just a quick scan of what networks are available and what kind of encryption if any.
Hawking HWL2 Hi-Gain WiFi Locator with USB Network Adapter and Hi Gain 6db Antenna It will set you back around $69, there are other options though.
DigiWiFi – Digital WiFi Detector
Mobile Edge MEASL1 WiFi Signal Locator