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Apple fixes its signal bars: Does it matter?

The intuitive visual message conveyed by signal bars may be meaningless in the context of how wireless networks work.
The intuitive visual message conveyed by signal bars may be meaningless in the context of how wireless networks work.
  • Some mobile tech experts question whether Apple's move is helpful or merely cosmetic
  • It might be more useful to think in terms of numbers, not bars
  • Experts say -51 dBm is the strongest signal and -113 dBm is the worst possible signal
  • Whether or not a cell phone has enough service to work is truly a yes or no question

Editor's note: Amy Gahran writes about mobile tech for She is a San Francisco Bay Area writer and media consultant whose blog,, explores how people communicate in the online age.

(CNN) -- Under fire for iPhone 4 problems, Apple has distributed an iPhone/iPad operating system update designed to display more accurate signal bars indicating wireless network strength.

Some mobile technology experts question whether this move is truly helpful or merely cosmetic. In fact, some have said the intuitive visual message conveyed by signal bars may be mostly meaningless in the context of how wireless networks actually work.

"Underneath the pretty graphical user interface, your cell phone measures those five bars in terms of decibels," explained Matt Braga of on July 1, before the iOS4 update.

"The closer that number is to 0, the stronger the signal, and the better available reception you have," he said. "However, as that signal weakens, the iPhone's UI chooses not to display that decrease in a linear fashion -- in other words, each bar does not represent the same number of decibels."

If you really want to know how strong a signal your cell phone is receiving, it might be more useful to think in terms of numbers, not bars.

According to Brian Klug and Anand Lal Shimpi at AnandTech, -51 dBm is the strongest signal most cell phones will report. "That's quite literally standing next to, or less than a block away from a tower," they wrote. "At the other extreme, -113 dBm is the worst possible signal you can have before disconnecting entirely."

So what's misleading about signal bars? Before Apple's latest fix, the original iPhone/iPad display would show five bars for any signal that fell in well over the upper half of the possible range of signals (from -99 dBm to -51 dBm). The first four shorter bars showed finer gradations in the smaller, weakest range of possible signals.

That's rather like counting from one to four, and then expressing the numbers five to 10 as simply "more." If you simply assume that "more" equals "five," you're likely to misinterpret what numbers one through four really mean.

After Apple's software fix, the AnandTech team did some field testing and published a follow-up post comparing the numerical meaning of the old bars versus the new bars. Now each of the five bars represents a similarly sized portion of the possible signal range, making the display more accurate.

Of course, the signal bar software fix does nothing to address Apple's notorious iPhone 4 antenna problem, which is a hardware issue. But for the typical cell phone user, does it help at all? Are more accurate signal bars useful?

Maybe not very. The main question cell users look to their signal bar display to answer is: "Can I send or receive a call and expect that it won't get dropped, send or receive a text or photo message, or get online with a reasonably fast connection speed?"

That's mainly a yes or no question. According to AnandTech, "With a few exceptions, signal power as low as -107 dBm is actually perfectly fine for calls and data. Below that is where trouble usually starts."

Mickey Papillon, host of The Cell Phone Junkie podcast, has long railed against signal bars as a meaningless visual metaphor. "It's a digital technology," he said on a recent show. "It should really just say 'yes' or 'no' you have signal."

In Gizmodo's summation of the Apple signal bar fix, Jesus Diaz quipped: "Free tip: If you paint flames on the back of your iPhone 4, it runs 2.3x faster."


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