Replacement sensor for ETL certified Carbon Monoxide Ventilation Controller COSTAR® 24VC-E. The sensor of COStar24VCe has to be replaced every 3 years. The detector will give a signal when sensor replacement is necessary approximately 6 months before its expiration (1 beep every 15 sec and green LED light flashing). There is a 3 year limited warranty on the replaceable sensor. Replacing this sensor module is very easy, just pull out the old and plug in the new. The sensor board is assembled, programmed and tested in America