How to tell how strong your iPhone's signal really is

Press the call button.

You'll see your normal signal bars disappear. You get these numbers instead.

But it's only temporary. Here's how to keep those numbers there permanently.

Once you see this screen, hold down the home button for a few seconds.

Now those numbers will stay there permanently. You can go back to the bars by tapping the numbers.

What do the numbers mean? The higher the number, the better your signal strength is. It's much more accurate than the signal bars.

If you see numbers in the -100s, be prepared for some problems making calls or receiving data.