They are always fail closed, if power is lost they close. They don't have to be on a dedicated circuit but it is a good idea. The end switches from them should kill the air handler.
No, they don't require any notification/alarming points.
legacy stuff, not necessarily.
chloride pyrotector systems have a fusible link that takes
a 12 volt small current, and ruptures a bladder inside a cartridge,
and it gets hot and melts the fire link in the drop chain.
resetting it, requires getting to the damper and putting a new fuse
link in, and wiring it in.
and, a 9 volt battery on an ohm meter, applied across those leads,
can trigger them.
i watched a journeyman drop a whole floor of them, one zone at a time,
while "testing" the system. every time he'd operate the test key, there
was this odd thumping sound.
he dropped about 80 zones in a hospital, three days before opening
of the hospital. 300+ dampers.
lotta overtime.