Characteristics:Siren for external installation with flash and with the possibility of connecting a 1.3Ah or 3.4Ah or 7Ah backup battery.Double cover: Outer – from 3 mm Polycarbonate with UV protection and inner: from 0.8 mm metal.Continuous frequency modulated sound.Tamper protection in 3 ways: Unscrewing central screw or tampering with outer cover or detaching from the support wall.Positive or negative trigger command.Separate input for flash only operation.