Here is a water sensor that helps you catch flooding in your home before it becomes a costly problem. The Fibaro Flood Sensor supports HomeKit, so it responds to Siri. It combines with your smart light bulbs to get your attention when there is a problem. It also has an acoustic alarm that alerts you when water is detected.
The water sensor can detect temperature and lets you know when you need to worry about frozen pipes. Costs under $70 at this time.