iOS 4.1 features: Field test mode

Field test mode, missing from iOS 4.0, makes its triumphant return in iOS 4.1. If you're not familiar with it, field test mode is a diagnostic mode that shows cell reception as actual, meaningful numbers as opposed to nebulous Apple and carrier rendered bars.

To enter field test mode, dial 3001#12345#

To exit field test mode, click the home button

If you're playing around with it, say trying out death grips, death touches, or AT&T death zones, lower (as in negative) numbers are worse. And if you're playing around, let us know your results.

(Note: I received an "error performing request" on my iPhone 4 under 4.1)


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Rene Ritchie

EiC of iMore, EP of Mobile Nations, Apple analyst, co-host of Debug, Iterate, Vector, Review, and MacBreak Weekly podcasts. Cook, grappler, photon wrangler. Follow him on Twitter and Google+.

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Reader comments

iOS 4.1 features: Field test mode


Aren't ALL signal strengths displayed as a negative number with -255 being no signal and -40 being the strongest, or 5 bars??

It worked for me on 3G running 4.1. Very interesting. I live in a rural area with no 3G and was in between -88 and -100.

Too bad it doesn't show any other information about the connected cells like it did on the past.

If you want to keep this mode active, you can do the following trick:

  1. Dial the code above
  2. When the phone enters test mode, hold the OFF button until the screen says Slide to Power Off. Let go of the off button.
  3. Hold down the HOME key and keeping holding it while you press cancel. Continue to hold the HOME key until you return to your regular screen.
  4. You should be able to use your phone normally while keeping Test Mode enabled.
  5. If you want to turn it off, just re input the code and then press the HOME key to disable.

thx for the tip to:

What should be a good signal number. Is there like a graph to show weak/medium/strong?
I got mine set to be on permanently now. I think I like numbers over bars ;-)

iPhone 4, IOS 4.1 works fine for me. In a town in Switzerland
With case on : on a stand getting -92
With case on : in right hand, i.e. finger grip over antenna join, -99
With case on : in left hand, i.e. palm grip over antenna join, -110
With case on : back on the stand getting -91
Without case : on stand getting -91
Without case : in right hand, i.e. finger grip over antenna join, -105
Without case : in left hand, i.e. palm grip over antenna join, -110

Great, after doing the permanent trick, I can't turn it off. Tried what it says but nope. The numbers are still there even after a reboot.

I can't turn it off either, however it allows me to tape on the numbers and it changes back to bars and then anytime I go into a webpage the numbers come back into signal but then back to bars.
It allows me to tap and choose what I want but I can't turn it off completely grrr

I tried the permanent trick but couldn't get it to work. But I double clicked the home button an d switched to another app and bam. The numbers stayed.

I want to turn it off permanently. I want the bars back permanently.
Who knows of a fix as the one provided does crap. Please tell me we don't have to do a complete restore and if so will it work lol

Only thing I can do is reopen the test page then tap the numbers, which gives the bars back, then close by hitting home button. Bad thing is when I open something the numbers flash then go back to bars.

Well this seems to confirm what anandtech reported, which is that any grip which covers the lower left antenna join results in about -20dB attenuation of the signal.

Just want to confirm the reset all settings worked. Would be cool if you could turn it off the way described.

I received a -111 with my vapor case on and -78 without. Ouch! I really like my case but it could explain my connection problems!

avg -79 to -84. Death gripped it's -108. Doesn't happen with my case, which I always use anyways. =)

This worked for me on iPhone 4 running iOS 4.1. My signal was -90 in my house. I live in the Detroit suburbs.

in central florida a little north of orlando: deathgrip with case off is -111, case back on and just holding the phone -97. after i put the phone into lock mode and checked it a minute later, -92. definitely supports that a case is recommended and no death grip

When the Attenuation issue and the death grip issues were flying I found an article in one of the IPhone forums that talked about what each bar represented as far as a decibel rating and more importantly what minimal decibel rating you had to have to maintain signal. Anyone have a link to it or atleast have this info?

Can someone please confirm Fantom's post which noted that - Aren’t ALL signal strengths displayed as a negative number with -255 being no signal and -40 being the strongest, or 5 bars??

Visit this link:
you will find accurate info on Keeping the Numerical Values and Bars, once you EXIT field test mode.
The info about hitting "Cancel" & holding down the home button is NOT accurate. Everything else about the process above is Correct. ONLY hold down the HOME button and wait for your home screen to appear and you have the best of both worlds. DO NOT click on "Cancel" & hold down the HOME button!!! This will only lead you to the VOICE CONTROL and more frustration.

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