IR sensors are sensitive to heat changes within the chip. That includes body temperature, but also a passing cloud within your property, etc. Using dual tech sensors, means it will only trigger when both IR plus microwave are detected, reducing false alarms. Other technologies includes ultrasonic, etc. I normally use Optex brand
I agree, I would use a proper outdoor sensor. I've got three PIRs to trigger the outside lights, two under a canopy and one near the front door, each makes an individual sound inside the house.
I've found too that cheap PIRs can be unreliable in windy weather, producing false triggers. My most reliable PIR is a Voltek 1816. It's not dual IR and microwave but relies on re-triggers in a short time frame. You can select 1 to 4 pulses within a 5 to 30 second time frame, and you would likely to need a control box which is an extra cost.
The Voltek website isn't https which is poor for a company selling security products! Be aware
Indoor IR sensors only, are designed for controlled environment, in which you may close a window or shade to reduce light changes, or eliminate the air flow within a room, that may move a curtain an trigger the sensor, etc.