It's probably there, up there at the ceiling or roof level.
If there's a suspended ceiling all you will see is the fire sprinkler heads but if you go out to a builders supply store, Home Depot is a good example, they generally don't have ceilings making it possible for you to see a lot more of the fire sprinkler system.
Take a good look, notice how sprinklers are laid out in a symmetrical pattern with specific spacing between sprinklers. Depending on the occupancy (use) of the building sprinklers are going to be laid out somewhere between 100 square foot per head and a maximum of 400 square foot per head. Generally speaking sprinklers are going to be spaced between 8 to 10' apart to a maximum of 20' again depending on the occupancy.
With sprinklers when we use the term "occupancy" we're not referring to the type of building structure or number of people that might be in it but the use, what is it used for? Motels, office buildings and hospitals are a "light hazard" occupancies meaning the combustibility of the contents is low allowing sprinkler systems to be "less robust" allowing greater spacing between sprinkler heads and smaller pipes.
Shopping malls and grocery stores are ordinary hazard occupancies that generally require closer spacing of sprinklers (130 square foot) and generally larger pipes while "big box stores" (Home Depot) and storage facilities require even closer spacing (100 square foot) and much larger pipe.
The questions are who does this work? Who actually decides a sprinkler need to go "right there" and "what size pipe" need to supply it? Who decided "how far down from a roof" a sprinkler has to be?
99% of the time these decisions are not made by the architect or engineer for the project. These decisions are not made by the people who do the actual installation. These decisions are made, and drawings prepared by, the Certified Automatic Sprinkler Layout Technician.
Layout Technicians are certified by the "National Institute for the Certification in Engineering Technologies" or NICET. NICET is a non-profit division of the National Society of Professional Engineers based in Alexandria, Virginia.
It's the certified layout technician that lays out sprinkler systems using architectural drawings of the project or by surveys conducted in the field for retrofit systems if architectural drawings are not available.
NICET certification in Automatic Sprinkler System Layout.
This certification program is for engineering technicians engaged in the layout and detailing of automatic sprinkler systems which must meet existing and proposed code and statutory requirements. Areas covered include knowledge of physical science, advanced hydraulics, applicable codes and standards, and contract administration.
Automatic Sprinkler System Layout comprises four levels of certification. Level I is designed for trainees and entry-level technicians who perform limited job tasks under frequent supervision, Level II is for technicians who perform routine tasks under general daily supervision, Level III is for intermediate-level technicians who, under little or no daily supervision, work with standards, plans, specifications, and instructions, and Level IV is for independent, senior-level technicians whose work includes supervising others. Certification at Levels II, III, and IV does not require prior certification at the lower level, but it does require meeting the certification requirements of the lower levels.