The SC Series ionization smoke detectors have a dual chamber design, so they automatically compensate for environmental changes such as atmospheric pressure, humidity and ambient temperature. A red LED indicator situated on the detector molding provides clear indication when the unit is in alarm. SC10U-3 detectors plug into the CSBU-1 base unit by a simple twist and lock action. In order to prevent unauthorized removal, a site selectable option is provided to lock the detector into its base. Once applied, the unit can only be removed by means of a special tool. All SC10U-3 detectors are monitored for detector removal. When a detector (or detectors) is removed from its base, a fault condition is detected.