the wigle wifi android app simply records all the wifi access points your phone sees as you are walking/driving about
you can upload your results to the shared wigle master database (https://wigle.net/), or just keep them to yourself, locally
you can query the db for open hotspots, or filter by security type
when you first run the app, every few minutes it has an annoying robot voice giving you stats (new networks detected, battery status, etc). it also plays sounds when networks are found. these can all be turned off (settings, and settings -> speech configuration)
the wifi scan interval has a few settings: stationary, slower than 8kph and faster than 8kph. pretty cool
the databases can also be exported to kml, and then loaded into google earth. i’ve previously parsed the exported kml into various layers (open, wep, wpa, cell stations…). interesting geeky fun!
the app itself also has google maps integration, and a search facility (for example to find the nearest open hotspot)