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See the actual strength of the iPhone’s cellular connection

This is a very old tip, but I’d never seen it before, so I figure it might be new to some others, too. My home has a relatively weak cell signal, varying between one and three dots on the iPhone’s display. But sometimes, even when I have three dots, the quality of my calls seems spotty.

While looking for some tool to try to analyze the cell signal’s actual strength in my home, I stumbled on this useful tip at Lifehacker: It’s possible to make your phone display its actual signal strength in decibel-milliwatts, or dBm. Here’s my phone, showing the stock display on the left, and the dBm value on the right:

And this explains a lot: While two dots of five seems like a decent connection, the actual value of -116dBm is bad. (Signal strength goes from a best of 0 to a worst of -140 or so.) How bad? According to this site, it’s an unusable signal. So, yea, don’t try to call my cell phone when I’m at home!

If you’d like to set your phone to display the actual signal strength (you can tap the indicator to flip between values and dots), read the above-linked article (or any of the thousands of other sites that have the same tip), or just read the rest of this post, where I’ve recreated the simple steps.

Here’s how to get your phone to show (and to stop showing) the actual signal strength:

  1. Tap *3001#12345#* on your iPhone’s dial screen, then tap the green Dial icon. This puts the phone in Field Test mode.
  2. Once you see the Field Test screen, hold down the Power button until you see the “slide to power off” message—but do not power it off. (Nothing bad will happen if you do, you’ll just have to start over.)
  3. Press and hold the Home button until you return to the home screen. You’ve just force quit Field Test mode, leaving your display showing the signal strength. Tap the strength display to alternate between the dBm value and the regular dots.

To undo this and permanently return to bars, tap that same number again—*3001#12345#*—on the iPhone’s dial screen, then tap the green Dial icon. When Field Test mode appears, just press the Home button to return to your home screen, and you’ll be back to the just-the-bars display.

15 Comments

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  1. Generally it is on…though your comment made me realize I hadn’t yet enabled it on my new iPhone. Just fixed that oversight.

    thanks;
    -rob.

    1. There’s a link in the article to a table that shows what the values mean. More negative means weaker signal, and below -100 is pretty low.

      Regards,
      -rob.

      1. Sorry I overlooked the link. That article states the accuracy of a phone display “might be off a bit with a $200 cell phone, but it should be close enough.” In my case, I can make and receive calls okay. Not claiming great quality, but better than the -103 might predict.

        Interesting article, thanks.

  2. It always bothers the geniuses when they see that display on my phone and think it’s a fault, till I explain.
    Anyone know how to enable the DBm display on wifi as well? It used to be an option in the old jailbreak settings tray.

  3. Pro-tip: You don’t have to undo the change as described above. Instead, just tap on the strength meter to toggle back to bars. Tap again to get back to the numeric value.

    1. I did mentioned tapping to cycle, but this is a temporary change: On wake from sleep, it will always default to the dBm number. To permanently change back, you need to follow the ‘undo’ instructions.

      -rob.

  4. I’m not sure how you’d dial the numbers on the mini. A quick web search implies that there is a field test app hiding on the iPad, but that you have to jailbreak it to get to it. Probably not worth doing.

    -rob.

  5. Any thoughts on an AT&T iPhone 7 giving a “Error performing request Unknown Error” with a Dismiss prompt?

    1. I have the same phone with the same carrier, and it worked for me. When does it appear?

      -rob.

  6. I have an iPhone 6S, and tried the above sequence. The phone went into Field Test, and I was able to get the signal strength display. However, no amount of tapping on the signal strength number will restore the bars.

  7. It’s an *amazingly* tiny target; way higher and closer to the edge than I would have expected. But it does tap, at least once you’re in permanent mode — I don’t know if it works when you’re still in Field Test.

    -rob.

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