are emergency exits still work during power outages. eg : the alarm will sound?

im pretty sure they will, if they are run on batteries. like in schools the EXIT signs are run by batteries and wont go off during a power outage. but im not sure about store alarms, i think they DO work cuz the only reason they wouldnt is because of a power outage, but that means the store owner is stupid because during a power outage, crime skyrockets, and they have to have alarms. na mean?

battery back ups are present on almost all security systems, but naturally, batteries don't last forever

Most have redundant backup systems, yes.

Redundancy would vary from location to location, based upon the percieved value of the protected area, and/or the assets available to the owner. Thus large chain stores would likely have battery power for longer than smaller stores. Same with say a Quick-e-mart vs a jewelry store. Common sense really, though I doubt looters are terribly concerned with common sense or security alarms anyhow.

good question

Here comes experience: My local school's alarm systems only last for half a day on battery backup. No more.

However, with your local high schools it might be very different. Are you the type of school that have Brand new metal detectors and 30 year old books? If so, then bet on a lot of security.