Where are the CO detectors? And why different CR123As?

What happened to the CO detectors?  Of course, I'd much prefer a combo Smoke/CO detector, but the CO detectors should certainly be available on the shopping side of the website, shouldn't they?  "Out of stock" I would buy, but they're not even listed - for either system.

I also noticed different CR123a batteries seemingly being recommended on the shopping page for the smoke detectors (panasonic) vs. everything else (duracell).  Why?  Personally, I use SureFire CR123a for all of my CR123a needs, and they're made by panasonic.  But really, what's the difference?