I have a sprinkler system, and a Rainbird wireless rain/freeze sensor.
https://www.amazon.com/dp/B011TMYBDO/ref=cm_sw_em_r_mt_dp_GTFYVNF1ABY9DHES3CHA
I noticed after the last few rains, it was not reading "sensor active", and stopping the watering program. Of course I took a look to see if it was full of spiders, spider webs or ants or just gunk. The old cork looking discs looked rather black and ugly, but seemed to function.
Pour water in the sensor and it would interrupt the system, but not very long.
So I started searching for the model of the sensor I have to see if Rainbird sold just the outside part. Nope, just the full kit with the indoor receiver and all for about $75 or so. So I kept digging.
I found this guy on Ebay:
https://www.ebay.com/itm/153523488818?_trkparms=ni_actn%3Anav%7Cni_nt%3AITE M_SHIPPED%7Cni_apos%3A1%7Cni_sg%3A1%7Cni_pos%3A1%7 Cni_st%3AREAD%7Cni_wh%3A1%7Cni_nid%3A478702231657% 7Cni_nsid%3A153523488818%7Cni_et%3A1626029676188%7 Cni_bn%3A1&_trksid=p2380424.m570.l5997
$6.99 sounded like a better deal, and no major risk. So I ordered, they arrived as they should, and it is easy to change them. Now we will see how well they work if it rains again.
I suspect the "rain gods" are confused right now. I did indeed just wash my El Camino today so ordinarily that brings out just enough rain to mess up the car, but the rain sensor waiting for a rain shower may cancel that. It will likely just rain on me the first time I am a few miles from home, and mess up the car but not rain at home.
With luck, the aftermarket will fix my issue for 68 bucks less than the Rainbird option.
It is nice to have options from the aftermarket.