Are mains  carbon dioxide alarms mandantory in new wires, and what are the main criteria for these. Same as smoke detectors?

Usually Carbon Monoxide (CO) for domestic, but no requirement in the building regs at the moment. Some commercial kit manufacturers (Apollo) make combined multisensors that include CO. Fairly new technology that isn't incorporated into many standard systems.

Generally AFAIK, carbon dioxide (CO2) alarms are only used in cellars in pubs or other commercial / industrial environments where levels of CO2 can build-up. CO2 detectors are often integrated into BMS and ventilation systems now to reduce fan / ventilation speeds according to occupancy and demand.

Paul

CO2 alarms only needed in houses occupied by secret lemonade drinkers