The Alecto SCA-02 is a package consisting of the Alecto COA-28/COA-26 carbon monoxide detector and the Alecto SA-19/1 smoke detector. The carbon monoxide detector detects carbon monoxide and the smoke detector detects smoke. The detectors produce a loud alarm signal of 85 decibels whenever the concentration of carbon monoxide gets too high, so you can act immediately. Both detectors produce a signal when it's time to change the batteries. The carbon monoxide detector also produces a separate sound and light signal when the detector itself needs to be replaced. The carbon monoxide detector runs on a 9V battery and the smoke detector runs on 3 AA batteries.Note: The specifications provided below are for the Alecto SA-19/1 smoke detector. For the specifications of the Alecto COA-28/COA26, please check the specific product on our website.