How do you know if your break pads are worn?

There are two ways to know if pads are worn. One is if i u hear a squeaking noise. Two is to look through the rim at pads and if u don't see any padding then need to change them. If u cant tell by looking through the rim then u will have to take the tire and caliper off to get to pads. If pad is more then half way gone or uneven then change them. If pads are uneven also replace the caliper.