Why does 9448 alarm go off on power cut?

Just moved into a house with an old 9448 alarm. Never had a problem until I was woken at 6am this morning after a power interruption and the alarm was ringing. Is the alarm supposed to go off with a power cut? Worried about this happening if I go away. Sorry I have no idea about alarms/electrics etc!

Also is there anyway of changing the amount of time that you have to exit the house after setting the alarm?