I have been using Irrometer Tensiometer analog gauges for years as a very accurate way to measure soil moisture. https://irrometer.com/sensors.html#irro
Irrometer has added an Auto Vacuum Switch (AVS) that basically works the opposite of a rain sensor - Normally “open” when the soil is moist - and then “closes” when the moisture is less than a preset threshold. https://irrometer.com/pdf/instruction-manuals/irrometers/716-AutoSwitch-Manual.pdf
This allows it to be hooked directly to a Rachio as a rain sensor using the rain sensor terminals/settings.
I am trying to keep a relatively young Arbutus Unedo (Strawberry tree) happy. It does not like the soil to be constantly wet - needs to dry out a bit between soaks. With the Irrometer AVS, the Rachio is set to drip daily for a few hours - Irrometer AVS being normally “open” will prevent the schedule from running most days. Once the soil dries out the Irrometer AVS closes and the schedule will run that day. Good so far, but the problem is that after about 50~60 minutes the water will eventually reach the Irrometer tip (down 24 inches) and trigger the Irrometer AVS and thus the Rachio rain sensor. It really needs to run the full 3 hours to fully saturate the soil.
The above would probably work if the Rachio (Gen 2) only looked at the soil sensor terminal a few times per day. The existing design checks very quickly (much less than a minute) and triggers too quickly for my needs.
I was never able to configure a Rachio automatic schedule that actually watered according to the strawberry tree’s needs that i could accurately see with the Irrometer gauge