Well there are two types of detectors,first one is that which operates with 9 v battery which one is cheap and simple , any one can install(just one unit)for each room with buzzer . Another one comes in set up to 8 -10 or more nos. of detectors with a panel and big buzzer/flasher ..that installation is expensive. Battery operated u can get in local market. Next thing, some are approved by QDC and some are not approved.. Its ur choice to install any.