We had to have the firemen drive the truck to the house in order to get the kids to feel safe again. They were great, got down to their level, and explained that they are smoke alarms rather than fire alarms and that smoke always comes before fire and that they alarms simply detect the smoke to warn everyone in plenty of time to get to safety.
They also warned of cobwebs and dead batteries. That's when we hunted down the spider and sent his soul home.