I will report practical experience of purpose built (wired) PIR sensors, intended for the 15m - 20m range. Both expensive 200 quid types, and cheaper chinese 20 quid copies.
Really good for pedestrians, in summer or snow or rain, I would say 95% reliable when aimed properly to avoid coverage gaps. With two sensors, entirely trustworthy… for pedestrians.
Can be set up off by rabbits and foxes and owls (we’re remote enough not even the farm cats stop by), especially when bunnies are frisky and run about. Harvest moon for false alarms, every year.
Can be set off by waving vegetation in field of view in right circumstances. Smarter PIRs try to tune out background noise, but this will never account for a sudden squall.
This is the apparent cause of our pedestrian “misses” - on a wild windy day, the auto desensitizing means it can miss a real target.
Only an issue if the field of view includes vegetation, obvs.
Can be blinded by direct sunlight into lens - choose position carefully.
Hit and miss for vehicles. Down to 30% success rate for fast moving vehicles (fast in this context, about 15mph, the target zone is a narrow gateway) on a rainy day. (my personal theory is PIR are most likely to trigger off the exhaust plume, which is smothered by cold rain and dispersed by speed - I have no experience of electric/hybrid targets but would expect rubbish results)
Microwave motion sensors should fare better here, no experience.
Compare to -
Infrared beams of reasonable quality (where the IR beam is encoded, not just light) -100% reliable and precise. Nuisance to install due to siting and wiring both ends - once.
Can in theory be set off by leaping foxes, cats or swooping owls - never happened yet to me.
For added confidence, I saw an army ammunition store upgrade its perimeter sensing just three years ago. I would imagine that is a “no expense spared” kind of job. They used these -
https://takex.com/photoelectric-beams-c-4632.php
These are NOT the same, but at one tenth the cost they work well