The most common sign on these newer, heavier Miramar Beach doors is the opener straining - you hit the button and it chugs, or the door stops a few inches up and reverses, because the motor is suddenly trying to lift the full weight of an insulated panel the spring is no longer helping to carry. On the older single-spring doors elsewhere in the area, a snapped spring often means the door won't budge at all; on these dual-spring setups, sometimes only one spring goes and the door will still limp partway open before you notice something's badly wrong.
Other signs: a loud bang from the garage (one spring letting go), the door hanging crooked in the opening instead of level, or a gap visible in one of the coils when you look up at the shaft above the door. None of these get better on their own, and a door running on one working spring out of a matched pair puts uneven strain on the opener and the remaining spring both.