I don’t see Zigbee on their list of certifications (per their website), and they only mention they comply to a 2.4 GHz IEEE 802.15.4 standard for their SMCDW02-Z sensor, but their PDF does mention Zigbee. The sensor model referenced in that PDF is from 2011, so it may be quite old. It may be that these devices only pair and work with their RB series touchscreens and supported systems? It also looks like they’re marketed towards cable operators and additional services they could provide vs the DIY’er market.
EDIT:
Looks like there’s a thread on this already, and perhaps these sensors (used by Xfinity Home and Time Worthless IntelligentHome) may be using their own version of an HA profile like Lowe’s?
More info: Open Home (battery life is impressive - 9.1 yrs!)
And, Open Home
Lastly, anyone notice the app CentraLite is using here (hint hint, about half way down):
http://www.centralite.com/index.php/products/3-series/3-series-door-window-sensor/