SmartThings vs Iris Motion sensors for use outdoors?

I think you’re likely to be very disappointed in any zigbee or Z wave motion sensor used outdoors in this way. You’re going to get a lot of false alerts unless you set them up as a zone using Mike Maxwell zone manager. You can try it, but most members have not had good luck with this use case.

The best outdoor motion sensors for this kind of use are probably the ones that are built into one of the outdoor cameras.