This article originally appeared in TidBITS on 2015-08-17 at 10:38 a.m.
The permanent URL for this article is: http://tidbits.com/article/15856
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How to See Your iPhone’s Precise Signal Strength

by Josh Centers

For decades, cellphone owners have relied on signal bars to determine the strength of the cellular signal. Since iOS 7, iPhone (and cellular iPad) users have become accustomed to signal dots, which do the same thing. But neither is a precise indicator, and you can’t necessarily predict what will or will not be possible when a particular number of dots are lit up.

Cellular reception in my area is awful, especially in my house. Sometimes voice calls work OK with one dot, but fail at three dots. Cellular data is even more unpredictable. My iPhone’s Internet connection often doesn’t work at all unless I have LTE coverage; 3G is almost as bad as no signal at all these days.

The folks over at Tech Insider have produced a video [1] that will help you see what your signal strength is numerically, for troubleshooting purposes. But for some reason, they didn’t also write up the instructions for those who prefer reading. So if you fall in that camp, here’s how to see your iPhone’s precise signal strength:

  1. Open the Phone app

  2. Dial *3001#12345#* and tap the green call button to put your iPhone into a secret Field Test Mode

  3. [image link] [2]

  4. Hold the Sleep/Wake button until the Slide to Power Off screen appears

  5. Release the Sleep/Wake button and ignore the Slide to Power Off prompt

  6. Hold the Home button until you go back to the Home screen

Instead of dots, you should now see a negative number in the upper left, like -102. This is your exact signal strength, measured in decibel-milliwatts, called the Received Signal Strength Indication (or RSSI if you want to impress technical support). The higher the number, the better, but note that these are negative numbers, so -1 would be an outstanding signal, while -1000 would be beyond poor. In the real world, you’ll probably see signal strengths somewhere between -40 (a five-bar signal) and -120 (a one-bar signal).

What if you get tired of trying to interpret the numbers? Tap the numbers to switch back to dots; another tap brings the numbers back again. And if you want to go back to dots permanently? First, restart your iPhone by holding the Sleep/Wake button, swiping the Slide to Power Off Switch to the right, and then pressing the Sleep/Wake button again to turn it back on. Then, to get rid of the numbers for good, go back into Field Test Mode and exit it by pressing the Home button.

I’ve been arguing with Verizon Wireless for years about my poor service, and have consistently received the runaround. The closest I’ve come to receiving actual help was being told to dial ### after a dropped call to mark it in Verizon’s records. (Give that a try the next time you lose a call!) But since standard cellular voice calls drop so consistently, I usually use Google Hangouts or FaceTime instead, and thus never have an opportunity to report problems. Sigh…

Now I can go to Verizon with this new, accurate information, and maybe someone technically minded will take me seriously. I’m not going to hold my breath.

[1]: http://www.techinsider.io/iphone-signal-reception-carriers-strong-field-test-2015-8
[2]: http://tidbits.com/resources/2015-08/Field-Test-Mode.png