I've heard that some AHJ are now requiring them as such at exit locations or exit corridors.

It should be a dry system as Jerry mentioned.

If its a wet, it could freeze or be subject to vandalism.

Say someone decides they would like to place an object with fire against the outside sprinkler head causing those in the house to go off and cause damages.

Just a thought.

__________________
I predict future happiness for Americans if they can prevent the government from wasting the labors of the people under the pretense of taking care of them.
Thomas Jefferson