iPhone Field Test Mode

I was investigating AT&T's signal strength in a specific location recently. On an Android phone getting a numerical reading for cellular signal strength was easy - Settings / About phone / Network.

But nothing is that easy on an iPhone.

But on an iPhone there's a really neat trick that is actually better.

Here is how the signal strength is normally displayed.

Dots.

Now go into the Phone app and switch to the Keypad like you were going to dial a phone number. Dial *3001#12345#* and press the Call button.

This will launch the Field Test Mode app and where the bars/dots were in the top left corner of the screen, you'll now see a negative number. The negative number is the decibel signal strength reading and should be followed by the carrier name and then the network type.

Bigger absolute numbers are bad. Remember these are negative numbers. -100dBm and lower down to -115 is sometimes iffy but mostly usable.  -90s OK,  -80s good, -70s excellent, and -60s off the chart fantastic

To exit and return your iPhone to normal status, all you need to do is hit the Home button.

But here comes the trick.

If you want your iPhone to always display numerical signal strength instead of signal bars, you can perform the following process.

Once in Field-test mode (accessed by entering and dialing the code above), hold down the power button until you see “Slide to Power Off”, then release it.

Then hold the Home button until you’re returned to your main app screen. Now you’ll see your numerical signal strength while you use your phone, and you’ll be able to tap the signal numbers to switch to signal bars, and vice versa.

To exit this persistent field-test mode, simply re-load Field Test Mode and exit it via the Home button.

Source: UberSignal

Update: This doesn't work in iOS 11.