What's the point of fire alarms?

I stopped putting fire alarms in the house because all it does is make sound in the presence of a fire. I already know there is a fire in the house. (This reminds me of that TV commercial from that credit monitoring company shows a bank robbery, but the security guard simply says 'There is a robbery' instead of doing something about it).

I never figured out the sprinkler system. They should introduce sprinkler heads like they had in sims 2. It worked every time.