This idea fills a gap in the market identified by the author: "You can buy many types of retro-fit devices to give your house a minimal smart-home capability. The most common of these are security devices such as magnetic and optical door and window alarms to detect intruders. These devices usually use an RF link to a controller and are really cheap, often less than $20 on eBay. By comparison water leak detectors are way more expensive; the price for a basic unit starts at around $50".
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