This may already be around but just in case it’s not I wanted to share my experience with the Xfinity Door/Window Sensors.
I recently purchased 2 lots of 10 Xfinity Door/Window Sensors on eBay, originally thinking I was taking a bit of a gamble on what I was getting and pairing/compatibility. I was pleasantly surprised when they arrived. All were new and unopened and they just worked. They were immediately detected in the HA Zigbee Add-On. I haven’t done any automation with them yet but there doesn’t seem to be anything stopping them from being successful.
Hard to beat for the price, 4.50 per unit. Lot of 10 XFINITY Security Visonic XHS2-TY MCT-350 SMA ZigBee Door Window Sensor | eBay