Field Test Mode for iPhone and Android

Your phone can tell you exactly how strong its signal is, in decibels, by entering Field Test Mode. How to enter Field Test Mode varies from phone to phone, but it is very straightforward and doesn’t require jailbreaking or in any way damaging your phone!

Most phone screens display signal strength in “bars” at the top of the screen. But “bars” aren’t a very precise measurement. Some phones (like the iPhone) have 5 bars, others (like the Nexus One) have 4. One phone might display a signal strength as 3 bars, another might only call it 2. To assess the level of signal an amplifier will be working with, we need to be a lot more specific. We need to determine exactly what the signal strength is in decibels (dB). Decibels are a very precise unit of measurement, where lower values means strong signal (so -60 signifies stronger signal than -80, -80 is stronger than -90, etc).

Field Test Mode for iPhone

iOS 11 update: Please see the video below for our in-depth guide to using Field Test Mode on an iPhone 7/7S with an Intel chipset. Phones sold on to users on the AT&T and T-Mobile networks typically include an Intel chipset, and have these model numbers:

  • A1784 and A1778 (iPhone 7 and 7+)
  • A1905 and A1897 (iPhone 8 and 8+)

Model numbers are written on the back of the iPhone in very small grey text under the Apple logo.

Unfortunately it is not currently possible to get signal information on phones running iOS 11+ with Qualcomm chipsets. Phones with Qualcomm chipsets are those sold to users on Verizon and Sprint, and have the following model numbers:

  • A1660 and A1661 (iPhone 7 and 7+)
  • A1863 and A1864 (iPhone 8 and 8+)

If that changes, we'll update this guide immediately.

Field Test Mode works for any other models of iPhone and any version of iOS, except the very original. Older versions of iOS display signal in “bars”, while more recent versions from iOS 7 and beyond display it in “dots”.
  1. Access the iPhone’s Field Test mode by typing *3001#12345#* in the phone’s keypad and press dial. This will bring up the Field Test menu.
  2. In the top left corner, you will see the numerical signal strength value, as in the picture below.

If you tap the number in the top left corner, it will toggle between displaying signal in decibels, and displaying it in “dots”.

To exit Field Test Mode and go back to your phone as normal, just press the Home button.

If you want to exit Field Test Mode, but keep the signal display in decibels, not dots, that’s easy. It’s particularly convenient if you are in the middle of a site survey and you want to move around from room to room to find the strongest signal. While in Field Test Mode, 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. You can now tap the signal dots or signal numbers to switch between the two. To exit this entirely and go back to normal, go back into Field Test Mode, then quit it normally by pressing the Home button.

Field Test Mode for Android

Enter Settings — About Phone. Your signal strength in decibels (dB) will be displayed under “Network” or “Status”.

An alternate navigation sequence for some Android phones is Settings – More Options or More Settings – About Phone – Mobile Networks – Signal Strength.

Older phone models may require specific codes. We’ve laid them all out in this PDF guide

As a general rule, -80dB or higher (ie, -70, -60, -50) is considered strong signal. -110dB or lower (ie, -120, -130) is very weak.