Or it could be a shorted cable.
Or a dead bat in the sounder.
Or it could be neither.
Remove the strobe trigger at the panel, see if that stops it.
Then in all probability the external unit has gone, but to be sure you would need to test the cables for a short anyway.
Remember there is mains inside the panel, if unsure call in a professional.
But dropping all power and then restarting is as good as pissing into the wind.
Alarm
December 2011