Hawks are vicious. We have a few families in my neighbors trees. I find half frogs, half mice, half bunnies in my driveway in the mornings. Obviously dropped from above. Just vicious.
There is a dry system also. Usually used in a electronics area. AS stated before by someone, I guess they might be used in non-heated areas too. Don't know. I haven't ever had the pleasure of seeing a dry system set off.
thats a preaction system, 2 sensors have to pick up the heat first before the line can be filled, once its filled the glass in the head has to go for it to be popped