WiFi Booster actually alters some of the Settings app’s WiFi options and making wifi scan more sensitive scanning even the weak wifi signals, which are otherwise not displayed. Apple sets a threshold on the signal strength of Wifi AP that decides whether a network would be connected to or not. WiFi Booster reduces the threshold at which WiFi hotspots are shown in Settings. By default, wifi hotspots with a guaranteed connectivity are set as a threshold, which actually hides even slightly unreliable wireless networks. But when you install WiFi Booster this threshold is removed, all networks are detected and can be connected to.
The app shows the signl level accurately in dbm so that you know what is stronger and by what measure. It also displays AP’s MAC address.
WiFi Booster can be bought from Cydia for $1.99 on a jailbroken iPhone.
See Wifi Booster in action: