If the alarm is in good working order, having the power off a few hours wouldn't cause any issues.
It's a common misconception that alarms sound if the mains goes off but that is actually a sign they are unmaintained and faulty.
PA would likely activate if connected, so you would need the code before you can silence it.
I assume any monitoring would be cancelled at this point but worth checking that too.
It probably says it wants 240v to
As a side note I was working with an IT engineer today who was replacing switches. They were 4 Yr old but end of life so being replaced. Nothing is expected to last as long as IA gear it appears