There are many home monitors fully suitable for intruder detection, but they’re not the kind you pick up sensors for for six dollars on Alibaba. Or anything made by Tuya. Or almost anything that works with SmartThngs.
these devices are designed and intended for home automation, even if they’re labeled security, and they just don’t meet the same quality standards as the purpose built security ones, which is why they don’t have UL listings for security or other independent third-party certifications, which would test reliability among other things. This has been true for more than 15 years. Sometimes you do get what you pay for. 
There are many high-quality Zigbee security sensors out there, but it’s just a different device group. And much more expensive. (Sea control4, for example.)
Also, this time of year, we always see a lot more false alerts on PIR motion sensors because with the season change two things are happening. Insects tend to be more active in the home. And there are drafts throughout the house at quite significant temperature deltas which can trigger the alarms even when no one‘s in the room. Also, late day shadows can do this. It’s because it’s getting cool outside. It’s warm indoors, the heat systems come on, the shadows fall and you just get a lot of temperature throughout the house.
The traditional approach if you want to use cheap sensors is to set up a zone of three or more sensors and not trigger an actual security alert unless all three of them report an issue.
Here’s an FAQ discussion from 2016 that’s still valid in concept although the exact methods will vary with today’s architecture. 
So the short answer is, if you want a good security system, buy a good security system certified by an independent third-party.
If you want to cobble together a decent cheap security system, using home automation devices, use the zone approach.