I have 2 smoke alarms 1 (smoke Battery) and 1 hotwire smoke w/ CO. We just burned something by mistake on the stove and both did not go off. Batteries are change every 6 months including hot wire model. I did a test and test passed and both are about 4 to 5 years old the max. any suggestion why? I most likely will buy new ones . Just asking.

They can go bad but both at the same time is strange. Try lighting a cigarette under one of them or a candle.

The smoke may not have reached detection level.