Some phones have a hidden function, which can be accessed by entering a code in the numeric keypad and pressing the call key. Once the number is dialed, a number will be displayed at the top left of the iPhone that expresses the quality of the telephone signal in dBm. If the value is close to or higher than -100 dBm the signal will be low and we will probably be at the farthest point from the neighborhood telephone repeater. The lower the value, the greater the signal received on the smartphone. Android users can view the signal strength or Network Management System in Settings> General> Device Info> Status.
Look for a nearby repeater with the apps. If in the big cities the telephone cells are widely distributed and available, it can still happen to find us in proximity of dead spots, hardly reached by telephone repeaters.
