We had a house fire several years ago. Previous owner had installed a hot tub in the back yard, with a separate fuse box for it attached to the back of the house. Husband had just taken our new puppy out for a potty-training break. A bug crawled into the fuse box (which, as it turned out, had recalled parts in it - how could we possibly have known?!?!) and it exploded, arcing electricity and flames up to the roof. I've never seen my husband run so fast. He came flying into the house and out to the garage, yelling at me to call 911, then raced back out to the yard with a fire extinguisher. My grandfather was a fireman, so I have several fire extinguishers located throughout our home. My husband had the fire out by the time the fire department got here. They sent heat-sensing equipment up into the attic to make sure it was completely extinguished. One of the firemen told us if we hadn't had that extinguisher, we would have, at the very least, lost the entire back side of our house. The fire had gone through the fuse box, through the aluminum siding, and into the insulation in the house before my husband was able to extinguish it.
We were very lucky - my husband was standing 10 feet away from the box when it happened, and we had a fire extinguisher on hand. I shudder to think what could have happened if the planets had not aligned...
Smoke detectors are a necessity, but I think fire extinguishers are a necessity also.