In iOS 4, Apple implemented an application called Field Test that allows the company's engineers to check the quality of the device's signal when testing it in the field or in various laboratory tests. This application is not normally available to users but by entering the code * 3001 #12345 # * in the Phone application in the Dialer and pressing Call you will automatically open the Field Test App. As soon as you open it, you will notice that some negative numbers have appeared instead of the signal bars. Those numbers indicate the strength of the signal and the higher the value, the "worse" is the signal registered by your terminal.
The application is available on any iPhone with iOS 4.1 (it was removed in 4.0) but on a 3GS with iOS 4.1 I only managed to start the application without having any information displayed on the screen. Practically, the application is not of much use for the uninitiated, but for specialists it offers information that normally cannot be displayed in iOS by the existing applications.
Those from Cultofmac have MEETS the application also in iOS 4.3, but they also discovered it through a simple search using Spotlight, which I could not reproduce. Moreover, they would have found a new version of the Field Test App that they know nothing about. It seems that Apple leaves the application "free" while testing beta versions and removes it when it releases the final version.
I was just performing a clear out of applications in my multitask bar on my iPhone, and I noticed one in there called 'FieldTest'. This isn't an application I've installed, and when I open it, it lets me do some things I don't understand.
