Basic BAS have five essential components:

Sensors — Devices that measure values such as CO2 output, temperature, humidity, daylight or even room occupancy.
Controllers — These are the brains of the systems. Controllers take data from the collectors and decide how the system will respond.
Output devices — These carry out the commands from the controller. Example devices are relays and actuators.
Communications protocols — Think of these as the language spoken among the components of the BAS. A popular example of a communications protocol is BACnet.
Dashboard or user interface — These are the screens or interfaces humans use to interact with the BAS. The dashboard is where building data are reported.

Most of the activity within a BAS takes place out of sight from a building’s occupants. The collectors are discreet, and the controllers and output devices are hidden from view, just as wiring and plumbing are.   _{Your Comment}