The idea is almost embarrassingly simple. A water filter already tells you when it's spent — it changes color. The only problem is that the filter usually lives somewhere you never look: a basement corner, a crawlspace, the cabinet under the sink.
So EyeOnFilter was developed as a small optical sensor that does exactly that: shine a light on the filter, read the reflected color, and translate it into a plain answer — dirty or not. Connect it to Wi-Fi and that answer follows you anywhere, including to filters at properties you're not even in.
The approach generalizes. Anything whose color or fill level changes — a soap dispenser, a birdfeeder — can be watched the same way. But we started with the filter, because that's the one quietly affecting the water a household drinks every day.