The next three symptoms are less obvious than a signal from a warning light; however, these signs of alternator trouble can tip off a driver that there's something going on that is out of the ordinary.
Mechanics are used to customers complaining of classic alternator issues, and then opening the hood to find the belt missing, hanging off the engine block, or so loose it's flapping around the engine compartment. Since a broken or loose belt is pretty obvious, take a peek under the hood to see if your car has any of these issues, even if you aren't skilled enough to fix them yourself.
If you're comfortable with basic maintenance and you're familiar with your car's components, you're in good shape to catch a problem before it leaves you stranded. A quick visual check of the belt for cracking, excessive wear, and other age issues can give an indication of a future problem. Keep in mind that the belt must have the proper tension to run the alternator correctly; too much tension is just as bad as not enough. A quick check of the belt tension is usually enough to determine if a problem exists. Make sure to let your car cool off before you start touching anything under the hood.