Standard voltage is 24 VDC
Way in the past, we have seen high and low voltage AC for some fire alarm equipment. We have also seen 12 VDC for some not as old equipment. As of now, the standard for all modern fire panels is 24 VDC, though some devices can operate on both 12 or 24 VDC.
Devices must be properly supervised
In no way can a devices be able to be pulled down from the system with out the system going into trouble. This behavior is critical to ensure the safest operation of the fire alarm system.
Devices may not be painted
Just because it may look a little nicer to have the device match the wall, this is not allowed. Please note that the device is to always be the color the manufacturer has shipped it as, and unless the AHJ says otherwise, lettering such as the word "FIRE" seen on devices may not be removed or covered.
The 'silence' button on the panel must disable both horns and strobes
This code is relatively new, and is not adapted in all areas as of yet. The idea is that a hearing impaired person would not know the difference between an active and a silent alarm if the strobes are still flashing. Because of that, NFPA 72 requires both strobes and horns to be shut off at the same time.
Synchronization is mandatory
For fear of seizures, all fire alarm strobes that can be seen at one time must be synchronized. Best practice is to synchronize the entire system so that no matter where someone is standing, inside or out of the building, all strobes flash at the same time.
Each brand syncs differently, and cannot be synced on the same circuit. Most alarms will not need a synchronization code in order to function, with the exception of Simplex devices. Simplex has two main kinds of alarms: Free Run, and SmartSync. Both of which require 24 Volts Filtered DC, which not every panel will do. SmartSync alarms will not do anything with out the proper sync code. Applying only power to a SmartSync device will leave you with a silent horn and no strobe until power is disconnected, at this point the strobe will flash once to discharge the power. A Simplex Sync Module or compatible panel would be required to overcome this challenge. These devices are only listed for use with Simplex systems.
Horns shall be a synced, temporal coding
Another relatively new code, horns on a fire system must do a temporal coding, sometimes referred to as Code 3. This is defined by NFPA as .5 seconds on, .5 off, .5 on, .5 off. .5 on, 1.5 off.
There are two key reasoning behind this. First of all, the pattern is very distinct and codes say that Temporal/Code 3 shall be used to define fire.
The other reasoning behind this coding is that theoretically, the pattern will motivate any occupants of a building to get up and move at a quick, but safe pace as it is not too fast, and not too slow. Our brains naturally will want to walk to the beat of the alarms.
***Please note that the rules listed above are very generalized. Local codes may vary***