I document things that expire in my house and October 31, 2025 I was sleeping and the carbon monoxide detector started beeping 5 short beeps. I woke up looking for what was beeping. Amazingly accurate 7 years until EOL and it was spot on! I replaced it the next day. I also replace my smoke detector batteries every 2 years else they wake you up in the middle of the night! Why can't these things fail during the day? :~)