You can fill your home with sensors that measure things like temperature, humidity, whether you left the garage door open, and who’s at home. Valuable as these are, there’s one sensor that stands head and shoulders above the rest in terms of the amount of money and hassle it can save you.

If you don’t have sensors hidden all over your house, do you really have a smart home? These devices make it possible to use all sorts of useful automations and alerts, from turning on lights to avoiding thousands of dollars worth of damage.