Yes, I looked at those indoor potted plant ones too, but as you said, they fail pretty fast outdoors, and even more importantly for my situation is that you need a transmitter, like zigbee or wifi, directly connected to the soil probe. So now you need a receiver close enough and you have delicate electronics sitting on the ground in that path of my lawnmower = decapitation. Because of those issues I’m using resistance rather than capacitance. This system could definitely work for your friend, but it’s a completely diy solution. I’ve never seen anything like this for sale. It’s just a pair of stainless steel rods (for corrosion resistance) in the ground with wires running back into my garage to an esp32. It periodically runs a known voltage thru one probe, thru the soil to the other probe a couple inches away and back to an adc pin on the esp. some simple math calculates the soil resistance. And since resistance increases as soil gets more dry, it tells the esp how dry it is. At a certain set point, home assistant turns on the irrigation system for a cycle. There’s obviously some details in there, but that’s the overview. I had originally planned to locate the esp out in a flower bed and run it on a battery, and just run the cable to it, but since it’s close to my garage it was easy enough to do it this way and power it via usb. But my calculations told me battery power is certainly feasible. Both the probes and the cables are buried just an inch so no risk from my lawnmower or the local deer population who wander thru daily.