The operation of double interlock systems is similar to deluge systems except that automatic sprinklers are used. These systems require that both a �preceding� fire detection event, typically the activation of a heat or smoke detector, and an automatic sprinkler operation take place prior to the �action� of water introduction into the system�s piping. Activation of either the fire detectors alone, or sprinklers alone, without the concurrent operation of the other, will not allow water to enter the piping