A pre-action system can be considered a single interlock and double interlock system depending on the system intentions and coverage. A single interlock system operates in a similar manner as the dry pipe system. This type of system has one event that must occur before water runs into the system; fire detection from a heat or smoke detector where the pre-action valve opens. A double interlock system has two events that must occur: 1) fire detection from a heat or smoke detector and 2) automatic sprinkler operation. Once one of the above occurs, the pre-action valve operates, allowing water into the system piping, essentially turning a dry system into a wet system. These types of systems are regularly used where unintended activation is not desired such as information sensitive environments.