Access The Hidden Field Test App For iPhone [iOS Tips]



Apple has hidden a field test app in iOS, which will allow you to quickly check the quality of your cellular signal by simply dialing a special code on your iPhone.

The code to dial is *3001#12345#* followed by pressing Call on your iPhone, which will launch the field test app.

The signal bars on your iPhone will be replaced by a number. The higher the negative number, the worse your signal is. For example, -100 is worse than -86.  If you tap on the displayed number, the display toggles between the number and the normal signal bars.

The remaining sections of the field test app contain a plethora of technical information beyond the scope of this tip, but might be interesting to look at if you are curious. The biggest thing to take away is the signal strength test, which can be very handy to know.

If you are done testing, simply press the Home button to return to your iPhone Home screen.

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58 responses to “Access The Hidden Field Test App For iPhone [iOS Tips]”

  1. ksdulin says:

    whats the best negative number you can have? 

  2. Timothy Williamson says:

    Interesting that they brought this back (guessing it’s an oversight) since it had previously been removed in one of the 4.x releases.

  3. Dan Y. Goldfeder says:


  4. Eric says:

    AT&T gives me -115 at home. Can’t wait till my contract is up. They told me around June that new sites would be up in October, they just told me that new sites would be up in March. AT&T is FOS they suck.

  5. Dustin Driese says:

    I have a -60 and have 4 bars of signal.

  6. nthnm says:

    So if I have -81 and 5 bars of service, does this mean it’s as good as it’ll get?

  7. Girts Dumpis says:

    jeezaz how many times old thing can be reposted?

  8. Guss says:

    no -81 is good but it will change as you get closer or farther from your serving cell tower. 

    As a rule of thumb wireless carriers use -76 as a good standard for indoor coverage, -84 for in vehicle and -92 for outdoor coverage. These levels are measured outside on street at head height (~6 ft) so if you got your -81 indoors your probably at -60 or so outside which is great!!BTW – the unit used here is dBm (Decibels referenced to milliwatts)

  9. Guss says:

    you can actually have positive if your in front of a tower antenna!! Having said that – you will likely never see that on your phone because the phone tuning sweet spot goes from about -30 to -130. Most carriers use a receivers have a min sensitivity of -102 to design their networks.

    Since these numbers are in decibel scales every + or – 3 is double the watts!!

  10. twitter-28439603 says:

    “The higher the negative number”.

    Uggh, someone doesn’t understand basic math.  The higher the *absolute value* of the negative number…..

  11. Bjohnson says:

    This doesn’t appear to work on a Verizon iPhone on iOS 4.

  12. Uu says:

    nothing happened with my4s too :P

  13. prof_peabody says:

    This doesn’t work for me either.  

    Probably it’s yet another one of those things where Americans think that they are the entire universe and don’t realise that this doesn’t work outside of their silly country. 

  14. Seth S. says:

    Yeah- that silly country where the iPhone was invented.

  15. Philip Rodger says:

    gotta put the * (asterisk or star) in the number you dial to get it to work. I missed it too the first time.

  16. Billgates says:

    in Calgary with Telus I get a -75

  17. MFD says:

    Doesn’t work for me in Southeastern Wisconsin on AT&T

  18. alcapone says:

    mine is -70 from DiGi Malaysia

  19. Jon Hernandez says:

    mine is -94 in Whittier, CA… 20 min from Downtown Los Angeles.

  20. José Chu says:

    My Brazilian TIM is giving me a -72 indoor in São Paulo

  21. Lumpany says:

    Works here in Australia. Must be an IQ thing :)

  22. FighterBobBrown says:

    Hey Peabody, in the lands where people can read and follow instructions, it seems to be working fine.  Please pack your anti-American prejudices back into your superiority bag and move along.  Thanks.

  23. Brandon Dillon says:

    Don’t be a wise-ass.

  24. Adrianwill0616 says:

    -102 AT&T Detroit. Smh

  25. Peter Reed says:

    -62 UK Manchester. o2….

  26. says:

    No joy on JB iPhone 4 running 4 on VZ or JB 3GS running 4.01 on Tmob.

  27. aga says:

    Works in the UK.

    Interesting, if I hold by the edges, I get -74. If I use the “death grip” I get -85. Looks like “antenna gate” has something behind it. That is in the city.

    Problem is, my SIM is Lebara (cheap overseas calls) which uses Vodophone as the carrier. Coverage is often very poor, so looks like I must watch out for the “death grip”.

  28. Todd says:

    USA iPhone 3GS iOS 5 on AT&T reports “Error performing request No Network Service”. Pretty sure I’m doing exactly what the article says. Also, yes I do have bars and 3G on AT&T. I’m not surprised, is there anything that works exactly the same way on every model iPhone?

  29. Todd says:

    Oops! Got it working. Make sure you don’t omit the * before and after the number. Somehow they are just hard to notice in the article.

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