SR-M04-SC Replacement BW Technologies Carbon Monoxide CO Sensor The SR-M04-SC sensor is an advanced in sensor technology called Surecell. Surecell sensors are the latest and most advanced sensors on the market today. Used in the GasAlert Extreme, GasAlert Quattro and GasAlert Micro 5 This is an OEM sensor. BEWARE! Use of a non OEM sensor will void the manufacturer warranty and may not work properly in your gas monitor.