Tool of the Week: Getting your phone to display decibles instead of bars

Here's a pretty cool trick that I tweeted last week:

Basically, instead of bars telling you how strong your signal is, you get a number with higher resolution and real units, which is awesome if you're even remotely mathematically minded.


So, Why would you want Decibles vs Bars?

Well first, you're not sacrificing your bars. You can always click the display where the signal strength is to toggle between the two.  But, knowing a few things about decibels shows why this is super useful!  The unit "decible" is a logarithmic unit comparing a ratio of two quantities.

Signal Bar maping, from

Signal Bar maping, from

The first cool thing about having signal in dBm is it's in actual units!  Notice the chart mapping bars to decibles: a weak 1 bar signal on an iPhone operating 4.0.1 or later has a range from -121 dBm to -107 dBm. Knowing this is a logarithmic unit: the range for "1 bar" is close to two orders of magnitude (7.94e-16 w vs 2.00e-14 w)!  That's a huge difference in signal!  So if you're walking around the woods looking for the strongest signal, but your phone is only showing you one bar, you're missing a lot of information!  So remember: With logarithmic units an increase of 3 is almost double the signal and an increase of 10 is 10x the signal.

The second leg up you're getting is you're not being suckered by whoever made your phone: notice how "bars" isn't a real function of signal strength, but is a gimmick that varies by phone manufacture.  What's not a gimmick is how strong each phone's receiver is.  The reason we "loose" reception is our phones receivers cannot distinguish between true signal and background noise.  State-of-the-art receivers can make this distinction down to -160 dBm (1e-19 w), where as most cell phones peatier out around -120 dBm.  Knowing the strength of your cell phone's receiver will greatly effect it's usefulness as a phone in low signal applications  (But good luck finding this info).

To perform this trick, if you have an Android phone, just go to settings.  If you have an iPhone, you'll need to access this secret app (Cue spy music).  Instructions are all over the internet, including at this lifehacker post:

1) Dial


and press call. Immedatly you'll be able to see how many decibles (in dBm) of signal you have, or switch back and forth between bars by tapping the signal strength indicator. If that's all you want, you can exit the app now by pressing the home button. If you want to keep this feature for good:

2) Hold down the Power button until the ‘slide to power off’ bar pops up. Do not power off.

3) Hold down the Home button you return to your home screen.

Many posts, like lifehacker say things like:

The lower your number, the stronger your signal—but don't include the - sign when evaluating (so, if the signal says -60, that's better than -90).

Actually: The larger the number, the higher the signal.  (So -60 is better than -90, because -60 is larger than -90).  Ignoring the '-' and saying a smaller number is better just makes you sound like an idiot.

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