Has a dead doorbell made you miss a visit from a friend or family member, or even a UPS delivery? If so, rest assured that you don't necessarily have to replace the entire doorbell system to get it working again. Check first to see if dirt or debris around the button is hampering its motion or preventing it from making contact. If buildup is the problem, apply rubbing alcohol or WD-40 to the button to clear the clog. If the button isn't the culprit, remove the chime box from its mounting bracket to inspect it, and grab a voltmeter to test it. If no signal registers, or if a signal registers but the chime doesn't sound, the culprit is either the transformer or the chime box, which you can replace or have repaired. Problems with the transformer are generally best left to the pros, though you can test the transformer by temporarily cutting the power and looking for any loose connections or disconnected wires.