Fire alarm systems are "Fire Detection and Alarm Systems" (FDAS). The NICET test is intended to show a command of the basics of DC and AC electronics, an understanding of fire alarm systems, along with a comprehension of the legalities of the "Code".
A fire alarm system is also a human made system; failures in the system are natural. Self-supervising for potential failures, alerting the owner of the failures, and sometimes having the system still working when the failures occur are a necessary part of a fire alarm system's being at least somewhat reliable.
NFPA 72 Code
Whereas the legal-ease shown in the NFPA's "Code" covers most of the issues, I'm not a lawyer, so I find it very difficult trying stick to the legal-ease of the "Code". NFPA (National Fire Protection Association, INC., actually a publishing house) understands that this is an issue for people like you an me. They have a Handbook that explains many of the legal-ease codes in the NFPA 72 Code.
The Handbook can be obtained on the official NFPA Website,
https://www.nfpa.org
In their website, the Handbook, "National Fire Alarm Code Handbook NFPA 72", is located right next to their NFPA 72 Code book.
Yes, the Handbook is more expensive that the Code book. However, I have found the Handbook to be an extremely valuable resource when trying to find answers in the NFPA 72 Code.
Get the Handbook: the Handbook will provide you with an understanding of the fire alarm system. Don't skip over the definitions near the beginning of the Handbook, either. The definitions in the Handbook will provide lots of information.
Electronics
Understanding the DC and AC electronics in a fire alarm system requires studying. Finding a course on the web, and studying, will provide help with the electronics part of a fire alarm system.
NICET Certification
Remember, the NICET Certification for fire alarm systems doesn't provide an understanding of fire alarm systems. However, when you understand fire alarm systems, NICET Certification shows others that you have this understanding.
Douglas Krantz