How do u do it?? The number
This will work on any iPhone model and any version of iOS, except the very original: Open the Phone app as if you were going to make a regular phone call From the iPhone keypad, dial *3001#12345#* and hit the “Call” button.
You will immediately see the signal numbers in the upper left corner, and you can tap around the menus to discover other random features and information that is generally meaningless outside of cell technicians and field operators. If you hit the Home button you’ll quit out of Field Test and the signal indicator will return to dots or bars rather than the signal numbers, but it’s easy to always see the numbers too as described below.
Enabling Signal Number as Reception Indicator Rather Than Signal Bars / Dots
To always see the signal numbers rather than the signal bars or dots, you’ll use the Force Quit app function to kill Field Test when it’s open:
Dial *3001#12345#* and hit “Call” if you haven’t done so already to launch Field Test
Now hold down the Power button until the “Slide to Power Off” message appears, then release the Power button and hold the Home button until Field Test quits
Tap the signal bars or signal numbers to switch between the two
To remove the tap-to-switch signal indicator ability, you can either reboot the iPhone or go back into Field Test and close out of it as usual.
In the newest versions of iOS, Field Test Mode transforms the signal ‘dots’ into the signal numbers instead, otherwise the feature is exactly the same:
The numbers mean this: The lower the number, the better the signal. Do -80 is better than -100.. Mine has been running about -97. That's about the same as 3 dots. -105 or lower is bad. You'll start dropping calls at -120.