NFPA 72 is the National Fire Alarm Code. It reads like code, not a text book.
www.nationaltrainingcenter.net has books you can use for test prep for NICET a common fire alarm technician testing agency.
I stated working in schools about 6 years ago and found fire alarms fascinating principally because almost all the circuits have two things going on at once:
1: a supervision done by low current or reverse current
2: a signal or alarm done by shorting or normal current.
This does not apply to more modern system (addressable) that are essentially computer networks that send messages around.
I found that asking intelligent questions of a really sharp fire alarm contractor got good, instructive answers, and eventually a xeroxed instructional handbook.
I got the installation manuals from various manufacturers and studied them and made measurements on live systems to confirm my understanding.
By the end I was finding faults in systems, determining the source of an intermittent but persistent false alarm, wiring fire/alarm elevator interconnections, installing long range photovoltaic detectors, and installing new complete systems.
All was made possible by study and a little mentoring by the contractor.
Good Luck, and have fun.
