dial *3001#12345#* from your iPhone. It places your phone in test mode. Then hold down the power button until slide to power off appears. Then hold down the home button until (do not turn off your device). Hold down your home button until you are back at your home screen. You have now changed your signal strength reading to decibels. The closer to 50 the better. 150 is BAD. here is a screen shot of my phone at my house. With -91 I usually have 1 bar missing. The bars are not an accuracy representation of your signal strength.