Just to clarify, the current code requires smoke detectors to be hardwired into the house. But, if the house was built before the code requirement, then you can install 10-year smoke detectors that have sealed, non-removable batteries (your second link). You replace the detector, not just the battery. Your first link to the battery would not meet this requirement, because it is for a smoke detector that uses removable batteries. Also, some experts recommend not using lithium batteries for smoke detectors because, even though they may last longer in use, when they fail, they fail very rapidly. Also, the lithium battery may have a 10-year shelf life, but most alkaline batteries claim to have a 15 to 20 year shelf life. I use alkaline batteries for smoke detectors.

Yes, my smoke/carbon monoxide detectors do (actually, have done) this in my house built in 2011. A specific pattern of beeps indicated the failure.

Isn't it something that the battery failure usually starts at night? I have been using Duracell Batteries and lately (Red Colored Quantum Batteries) most of my life with no problems but the last two batches from Lowes on 441 have failed very quickly in the Smoke Alarm/ Carbon Monoxide Detectors. I still stuck to Duracell but went back to the Gold & Black Color batteries.

I added 3 Fresh/New units after I bought the Gas Powered Generator. Better safe than sorry.

Maybe added by the previous owner?

I still don't understand why they just don't keep beeping every 10 seconds or so until I get my hands on that little ba_____. Old people games!

Here's what is being installed in the new homes.

The CPSC determined the cause for lithium failures the was a high internal resistance in the batterys tested and subsequently changed the recommendation once root cause was corrected. But I would only use batteries certified by the manufacturer for smoke alarms.

https://www.ultralifecorporation.com...hitepaper.aspx

Post No. 8 has a link to the user manual for that smoke detector.

Both lithium and alkaline batteries are certified for use as back up batteries in hardwired smoke detectors. In fact, the First Alert smoke detector shown in your Post No. 21 comes with an alkaline battery installed in it, not a lithium battery. I believe this is true for most smoke detectors with back up batteries on the market. I think that the Ultralife company is using their lithium battery packaging as a sales gimmick to sell the more expensive lithium batteries. Also, if you are going to replace the batteries every year as recommended, then why would you need a 10-year battery anyway? But, alkaline battery makers actually claim that their batteries have a shelf life longer than 10 years, and they are recommended for smoke detectors. I would also point out that Consumer Reports recommends alkaline batteries for smoke detectors because, when they fail, they have a longer voltage dropoff period than lithium batteries, which prolongs the low battery warning beeping time. They specifically recommend against using lithium backup batteries in smoke detectors for that reason.