Review on YoLink Smart Motion Sensors, 1/4 Mile Range Wireless Indoor Motion Detector, Alexa IFTTT Compatible, App Alerts & Remote Monitoring, 2 Pack with YoLink Hub by Raffy Baer

Exactly what I was looking for and a lot smaller than I thought it would be. Setup took less than 10 minutes: download the app, connect the hub to power and Ethernet, press a button on the sensor, and you're done. Installation was just as easy, pick a good spot, test it as best you can before making it permanent, then just peel off and insert the magnetic plate to make it stick. Integrates directly into Alexa routines or ifttt via skills and the app has its own setup for scene creation and automation. I didn't check their pairing with Smart Life, but it wasn't necessary, Alexa receives the motion detected event and triggers Smart Life scenes or devices as needed. Smart devices can vary wildly in quality, but they're just plain reliable. I'm not worried about adding some door sensors from these guys.