As you probably already know from the past years, iOS offers us the possibility to numerically display the GSM signal strength of our iPhones, replacing the well-known bars/dots. In the iOS 7 Apple Lossless Audio CODEC (ALAC), did not eliminate this functionality, but the changes implemented by the company involve the use of a trick to display what we want. Basically, open the Phone application, type in it *3001#12345#*, press Call, and in the next second the application below (Field Test) will open, which will give you all kinds of information about the GSM signal.
Opening this application will force the numerical display of your iPhone's GSM signal, but when you close it, everything will return to normal. To avoid this, you will have to hold down the power button for a few seconds, and when the shutdown menu is displayed, you will have to hold down the Home button for a few seconds, and the application will be closed and the signal will be displayed numerically. Any value below -100(-85 – -99) indicates that you have a strong signal, and any value above -100 indicates that you have a weak signal.
