A home should be fitted with multiple smoke detectors (obviously depending on the size of the place). Each, occupied, floor of the home should have at least one, this would include the garage and basement which is where we usually store most of our flammable items. It is a good idea to have one in each bedroom as well.
Knowing what to do incase of a house fire is another essential step to surviving one. The entire household should be educated about what steps they would need to take. It is a good idea to have a practice fire drill, preferably at nighttime when the household is asleep, as this is when they are most at risk. Set off each smoke alarm to see how effective they are at waking the household, particularly children, then instruct them about what to do next. Its important for the smoke detector sound to be distinct enough so that it is not confused with any other sound found in the home and loud enough to wake even the deepest of sleepers.
One of the biggest reasons smoke detectors cease to be effective is the batteries. This is a very simple thing to check. Once a month, go through the house a check to see if they are working correctly. Another big reason is that someone has disconnected them and forgotten to reconnect them. This can easily happen if the smoke detector goes off due to cooking etc. NEVER disconnect smoke detectors.
From this brief review, we can see how vital smoke detectors are, but they need to be checked to make sure they work properly.