The little blue light on rings comes on when they pass, then when they go to check it out it makes a noise when it starts recording. By cat standards that's a toy
Bingo! I live in an area where there's lots of wild life, including cats (they don't appear to be owned by anyone) that roam through our neighborhood.. we have a camera where an LED lights up the moment there's detection, cats and racoons are more likely to approach and analyze.
I'm not sure why you think that would be an issue. Mounting the exterior compressor close to the ground is common practice for ease of maintenance. Getting it wet isn't really a problem. I'm not really sure why we're having HVAC install discussions in a cat forum though :P
Most mini split installs I've seen are not so low. The lowest I've seen is at least a foot off the ground until now. Maybe it's not a problem for them.
Cats also have insanely sensitive and wide frequency hearing. It might notice some sort of coil or switcher whine or other noise that wasn't there before.