A simple code can allow seeing hidden information your iPhone, as well as giving you permission to make changes to its private settings.
The iPhone’s Field Mode is a largely hidden but useful tool that allows you to see extra information about how your phone is connected to the internet.
The tool is enabled by dialing *3001#12345#* and then pressing the call button. Your phone will switch away onto a grey screen, after which you’ll see the extra information.
One of the most useful features is a more detailed signal strength indicator which should appear in the top-left hand corner.
Anything above -80 is roughly equivalent with full bars on the normal scale. Anything below -110 would be one or no bars and you are unlikely to be able to easily make a phone call.
In practice, the maximum strength ever achieved is around -40. No reception at all is around -120, though it goes all the way to -140.
If you want to keep that number in the corner, rather than the usual dots, then hold down the power button. The message to turn the phone off will appear, and then press the home button.
The feature should then be enabled. Users can switch between the two ways of viewing the signal by pressing on where they display, in the top-left hand corner.
There are a range of other codes that offer other information.
Using *#33# will show the status of your call barring settings. That tool can be turned on and off using *33*pin# and #33&pin#. Swap PIN for your sim PIN.
Using *#43# will tell you whether or not call waiting is turned on. That feature allows people to queue up when they ring you, so that the phone can alert you if someone is trying to get through while you’re already on a call.
It can be turned on using *43# and turned off again with #43#
*#06# will show up your IMEI identifier number. That’s very useful because it can be used to shut down your phone remotely if it stolen, but it can also be accessed from the Settings app or on the phone’s box.