"...nothing was taken from the store and the alarm may have been the key to scaring the would-be thieves away." When the alarm starts wailing, they know that the auto-dialer is calling the police and everyone in the area is paying attention to that store. They leave immediately, without stealing any...ahem..."AK-57s"... If you're business doesn't have an alarm system, you may as well hang a sign out front that says, "Come steal my inventory."