Abstract: A static fluid system for detecting a selected change in an ambient condition. The system includes an elongate closed fluid line having a selected absolute pressure and pressure means to maintain the line pressure. Sensing means in the line respond to selected changes in ambient conditions to open the line and change the line to ambient pressure. Signal means responds to the change in line pressure, and flow restricting means in the line maintains the line pressure under normal ambient conditions and precludes re-establishment of the line pressure when the sensing means is activated to open the fluid line.

Abstract: An alarm system comprising an elongate and flexible pressure line adapted to be charged with a selected line pressure; switching means coupled to the line and responsive to a pressure change in the line to create alarm signal; union means inserted in frictional sealing engagement within said line and having a bore which maintains the fluid continuity of the line; and spring-biased retaining means circumscribing said line and applying a selected clamping force to seal said union means in said line. The union means are arranged to break the seal of the line in response to an emergency condition, to thereby lower the line pressure and activate an alarm.