No idea about warranty. BUT...
2:00am today, from my bedroom, I heard the dreaded CO/Propane alarm through my bedroom wall where my Dweller is in the driveway (about 20ft from my head in bed; it's a loud alarm). I have replaced the sensor and wired in the 1A inline fuse and hadn't had a problem since I'd done that. It didn't go off again. I took an hour to get back to sleep, thinking about how I was going to handle that in the morning, calling the sensor company, not OBI (which is relevant to the warranty discussion).
4:00am today, it goes off AGAIN! I'm wide awake now, and pissed, so I throw on some sweatpants, grab the key, and go take out the inline fuse. I know it's not CO or propane because nothing is hooked up. No lights flashing on the sensor. I'll just disconnect it and deal with it once it's light out. I get back to sleep after another hour.
5:45am today, my alarm goes off and I get out of bed, very grumpy.
6:00am today, it goes off AGAIN!!!
Turns out the battery on my work pager in the living room was low. (Yes, I have a pager; no, I'm not a drug dealer.)

CO sensor is fine.