how do smoke alarms help?

I Cant find anything so can anybody please help

It warns you that a fire has broken out, or if there is too much smoke in a room. If especially works if people are sleeping and a fire breaks out. It warns them and give them time to escape.
it tells you if there is a fire, if you didn't have a smoke alarm; then you could mostprobably end up dying, because fire burns and if you inhale smoke then you end up with breathing problems; this is why we have smoke detectors so that if a fire does break out, you can exit from the building before it gets too troublesome...