The iOS 4.0.1 update is out. It claims to “improve the formula to determine how many bars of signal strength to display.”

From my initial (admittedly anecdotal testing), I can confirm a difference in the number of bars displayed. Whether or not the difference is an improvement, I suppose can be debated.

My iPhone includes the Field Test modification that allows me to toggle the status bar to display either bars or a dBm number. [Note: If you haven’t already made this change, you can no longer directly do it with an iPhone 4 (as noted here). I was able to retain the feature by restoring my iPhone 4 from my iPhone 3GS backup, which already had the change included.]

Bar shifts. Using this dBm toggle, I can confirm that dBM numbers that formerly were linked to a 5 bar display, now display less bars. For example, dBMs in the range of -85 to -95, now show 3 bars on my iPhone. Previously, they showed 5 bars.

dBM shifts. Interestingly, iOS 4.0.1 also seems to have changed the way the iPhone reports the dBms themselves. Typically, I get fairly poor 3G reception in my office. Previously, my iPhone 4 would often show dBms here below -100, more than occasionally sinking to -113. Now, my iPhone’s dBm numbers almost never sink below -96 and have gotten as high as -78 (a level previously never achieved in my office). By the way, the -78 corresponds to 5 bars.

Does this mean that the reception is actually improved as a result of the update? Or simply that the method of reporting dBms has changed? It is too early for me to say for sure. But I suspect the latter.

Signal strength loss. The big question: What effect does the update have on the loss of signal strength when you hold the iPhone in the “wrong” way? My quick testing suggests that there is not much change. I still see about an 10 – 12 dBM drop off when I squeeze the iPhone in the prescribed manner. Using a Bumper case prevents this loss. However, because the dBM levels are (apparently) improved, the drop off doesn’t descend to the borderline -113 level anymore.

iPad update. Apple also released iOS 3.2.1 for the iPad today. The update “improves Wi-Fi connectivity” as well as fixing a couple of other minor bugs. Interestingly, the update makes no mention of modifying how 3G bars are displayed. Does this mean that Apple believes that the iPad’s method of displaying signal strength is not subject to the same errors as the iPhone? I don’t know. As far as I know, Apple has not commented on this.