E2S Warning Signals has developed a SIL 2 version of its flagship BEx range of explosion proof alarm horn sounders and Xenon strobe beacons. The company says its new IECEx and ATEX certified BEx horns and are designed and tested to ensure a 99.9% reliability rate, bringing plant safety to new levels. To meet the requirements of SIL 2, a combination of software and hardware in the new units monitors and interprets the sound output of the horn or the light output from the Xenon strobe to check it is functioning correctly. The fault monitoring reports back to the control panel utilizing either separate fault contacts or by the introduction to the monitoring circuit of a series resistor. Using the series resistor facility eliminates the need for any additional cables and can be used in a standard two-wire arrangement.