There are two community discussion threads on outdoor motion sensors which are worth looking at.
The first one is pretty short and basically just suggests putting a tube over the lens of a PIR motion sensor, any of them including the Aeon which at least does have a weatherproof case, which can reduce some of the false alarms just because you narrow the detection field. But it obviously won’t work for all use cases. It’s most useful for use cases that involve small detection areas, like wanting the front lights to come on as you approach the front door. Not so useful if you want a security warning over a larger area.
The second is a long detailed discussion about the issues involved in using outdoor motion sensors and what some of the options are. There is some good information there, including suggestions from some of our UK members, but the short answer is to choose a device which is designed for outdoor sensing and then Wire it to something like the Aeotec Dry contact sensor (available in both the US and the UK) to have the reports sent to SmartThings. The thread discusses several different types of devices and different wiring methods, as well as the use of @Mike_Maxwell 's zone manager smartapp to combine several sensors into one zone. So different people will find different parts of thread helpful depending on the details of what you are trying to accomplish.
Still another option is to take advantage of motion sensors built into more expensive devices like the ring doorbell that @tyler mentioned or some of the outdoor cameras. These use a different technology than the simple PIR sensors and consequently have fewer false alerts outdoors. This option won’t work for everyone, but some people will find it useful. 