If you commit unintentional herbicide more than you’d like, there’s a good chance it’s because you’re watering your plant an inappropriate amount. If this is you, or if you just can’t stand to have something natural in your house without a bit of technology attached, then the Chirp! plant watering alarm may be for you!
As described in its writeup, “You put it into the soil near a plant and it emits a tiny chirp when the soil is dry, reminding you to water the plant.” At this point, you will water the plant — yes to keep it alive, but more to stop the sound. It is, however, programmed not to chirp at night, so it should be less annoying than some other household alarms.
If the design doesn’t work for you, it’s open source, so you can make changes as needed. As is though, it should be easy enough to use for even the worst gardeners. Be sure to check out Catnip Electronics’ page for a slightly different version of this sensor, a couple of other electronics bits, and a black-and-white picture of a computer scientist with a cat’s head!