View source for Iphone

If you type 

 *3001#12345#*

in an iphone and hit call it pulls up the secret field test app. you will notice instead of bars for signal strenght you have number. The close to zero the better the signal. Hold the lock button until the turn off slider appears, but don't turn off. Now hold the home button until you get back to the home screen, and there you go. 
Tap the number and it will change back to bars and vice versa. A lot more accurate than the default of bars.

If you happen to be in a frozen app, instead of turning off your iPhone entirely, just hold the sleep button until the shut down screen appears then hold the home button. Your app will have been force quit.