Thanks for the replies with regard to motion and false positives.
I considered PIR at one point, but it strikes me as cost prohibitive for larger installs.
The decent outdoor sensors appear to run $150+. Add in the cost and difficulty of running 12V power to everything, and I'd rather spend the extra money and go with one of the high end commercial products (Mobotix) that can do intelligent motion detection via video analysis. The addition of two way audio (plus built in PIR detectors on some models) makes it absolutely worth it.
That being said, I certainly have my issues with Mobotix. In addition to the insanely high prices, I actually find the video quality during the day to be inferior to the Hikvisions. At any decent resolution, framrate suffers badly.
In particular, the way in which they blow out in dealing with light colored objects is unacceptable, especially at that price. Carl (Network Camera Critic--RIP) nailed it when he stated fairly recently that Mobotix was incredibly impressive five years ago, but that it appears that they have stood still while the rest of the industry caught up and passed them by.
The Chinese cams have come a long way with regard to image quality over the past couple of years. As I have pointed out on other threads, what we need right now is not 4K, or any other increased resolution. Instead, the two biggest issues are:
1. Reliable motion detection; and
2. Night performance.
Instead, the manufacturers seem to be engaged in a pixel count race.