A few weeks back I posted about finding the signal strength in decibels (dBm) on an Android phone, and I promised then to post similar instructions for finding signal strength on iPhones. So here we go.
It’s often useful to know how strong a signal your iPhone is receiving. As pointed out previously, if you’re trying to make a call but it won’t go through or if you’re otherwise not getting the cell service you expect, then knowing your signal strength can help you determine why not.
Of course virtually all phones have the “bars” or “dots” graphic that displays on your home screen, supposedly so you know what your cell phone signal strength is. The problem with that graphical representation is that it lacks any kind of standards.
The accuracy of the dots can vary widely, so viewing your iPhone’s actual signal strength reading is always preferable to relying on the dots graphic. Signal strength is typically measured in dBm, a standard unit of measure. By accessing the decibel reading on your iPhone you know with certainty how strong a signal you are receiving.
While Android phones allow the user to view signal strength readings by navigating the menu tree, with iPhones finding the decibel reading is a bit more complicated. You must enter a sequence of commands to put your iPhone into ‘Field Test’ mode to display the dBm reading.
iOS 9 FIELD TEST MODE INSTRUCTIONS
If you have updated your iPhone to iOS 9, follow the instructions directly below. These instructions are specific to iOS 9. If you’re using an earlier version of iOS, those Test Mode access instructions are further down in the post.
dBm is typically expressed as a negative number, -88 for example. The closer to zero the reading is, the stronger the cell phone signal. So for example, -79 dBm is a stronger signal than -88 dBm. A reading of -50 is the strongest signal you will see. When a signal is weaker than -100 dBm, that’s a pretty weak signal. If the signal gets much weaker than that, you likely won’t have service.
If you don’t want the dBm reading to display on your iPhone home screen, you can dial the sequence again and just hit “back to phone” and it’ll return to the dots graphic.
FIELD TEST MODE INSTRUCTIONS for earlier iOS versions
The instructions below have worked for iPhone 5 models and newer up until the iOS 9 release.
Your screen will show “Test Mode” and the dBm reading (as a negative number) will display in the upper left side of your screen.
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