IMO this alarm should be OFF by default. It's really a useless feature, and every Volt owner should be instructed to turn it off. It's actually bad for public plug etiquette. The other day, the Volt next to me had a sign on its window saying it was ok to unplug when it was done charging, but they didn't turn off the alarm! I unplugged it so I could charge, but the alarm goes off and is super annoying. There were tons of people going in and out of the lot, but nobody cared. It doesn't even last that long (and thank god it doesn't!) So, other than annoying people, it's almost totally useless.
The only SORT of use I can see is that it's supposed to alert you to when someone is taking your charge cord if you're using it at home. Nobody cares about the alarm except to be annoyed by it, but at least that might alert you to someone unplugging your cord while you're in the house. But in this case, what it really should be tied to is the location-based charging, so that it only arms at a set location like your house.