Under a state-wide law as of 2009 sprinklers are required in new construction townhouses and as of January 1st of 2011, all single-family residential homes need sprinklers. They are the same sort of sprinklers that are in hotel rooms - when the temperature reaches a certain level, they burst and spew water. There will be multiple sprinklers in every room.
The sprinklers are meant for personal safety- to defuse a flame for example and not for property protection. They would not be strong enough to extinguish a blazing fire but would provide enough water to sprinkle a flame.
Once the sprinklers are installed, they are not checked. It is up to individual homeowners to make sure they continue working.
According to Michael Como, Chief Plumbing Inspector for The Allegheny County Health Department about 1,000 new homes were built in the county last year that required the sprinklers. He did not know how many of those houses are occupied.
He is working with sprinkler companies and home-builders while they install sprinklers in these houses to ensure that they maintain codes. He is also working with other counties to learn about their sprinkler installation techniques.