3M Scott Safety Inline Whistle with CEN Couplings. Constructed from nickel plated brass, with 1 Female Socket CEJN type coupling and 1 Male coupling to allow quick and easy interfacing with the airline hose. The medium pressure warning whistle allows an inline warning to be added to the system to notify the user that the airline pressure is dropping. The activation pressure of the whistle is 3 - 4 bar.