The 429C Series self-diagnostic, Two-wire smoke detectors continually monitor their own sensitivity and operational status and provide a visual trouble indication if they drift out of sensitivity range or fail internal diagnostics. They meet NFPA 72 field sensitivity testing requirements without the need for external meters. Features: Intelligent, self-diagnostic * Field-replaceable optical chamber * Low-profile design * Plug-in terminal block * Advanced false alarm immunity * 12VDC and 24VDC operation. (Not Compatible with Caddx Panels). GE Interlogix.