8. The Brittle Ice Alarm Floor
Brittle ice cracks when you stand on it, and it keeps cracking until it breaks. That’s a hazard — or an alarm system, if you’re clever. I laid a strip of brittle ice across the only approach to my front door, over a shallow pit with a ladder back up. When something heavy walks across at night, I hear the cracking. It’s not perfect, and yes, I’ve set it off myself at 3 a.m. carrying diamonds. But as an early warning, it’s free and thematic. Just don’t forget it’s there.