I’ve made a habit of only ever looking at signal level in numerics on iOS since the iPhone 3GS days. This has paid off a few times in the past (notably the iPhone 4 antenna situation) but in general just gives a better perspective for network conditions. I regularly post screenshots with both cellular and WiFi in numerics instead of the default bars, and on iOS this is pretty simple to make happen, at least to the cellular signal level indicator, without jailbreaking.

To do this the basic workflow is to enter FieldTest.app, then force quit the application. When FieldTest launches, it changes a .plist file for springboard which controls whether numerics are being shown for cellular signal. This is exactly the file that SBSettings tweaks if you’re toggling “Numeric GSM” and “Numeric WiFi.” I should note that these settings also stay around across iOS restores. Anyhow a lot of people have been asking on Twitter lately for some reason how to make this happen, so I thought I’d write it up.

  
Dialer for FieldTest (left), FieldTest.app (right)

Anyhow to show cellular signal without using SBSettings:

  1. Launch FieldTest.app by going into the dialer and dialing *3001#12345#*
  2. Hold down standby/lock like you’re going to turn the phone off
  3. Release standby/lock after the power off slider appears, then hold home (this is force quit on iOS – it’s impressive so few people know it)
  4. Boom, you have numerics instead of bars

This can now be tapped to switch back and forth. Launching FieldTest again and quitting will restore the file however, so every time you quit this will have to be a force quit to preserve the setting without jailbreaking or restoring an iOS backup with the plist file set how you want it.

I should also note that on LTE this number is RSRP (Reference Signal Received Power) in units of dBm. On WCDMA this is RSCP (Received Signal Code Power) in dBm, and on CDMA2000 1x/EVDO this is RSSI I believe (or EC, I haven’t ever carried a CDMA2000 iPhone for an apreciable amount of time). On WCDMA and 1x/EVDO values between -50 and -113 dBm are typical, with -50 being at cell center and -113 dBm being at cell edge. On LTE because the iDevice is showing RSRP, values between -75 and -120 dBm are typical, with RSRP showing ~20 dB lower than the analogous RSCP/WCDMA-land signal if you’re trying to compare.

Update/Note: In iOS 7 the signal bars were changed to dots, but the trick still works. Although switching into numerals by force quitting Field Test still works, sometimes it takes a few tries before it works. I’m not sure why that is, but keep force quitting or try quitting and coming back and force quitting again and eventually you’ll switch over.