When it’s opened, hydrogen peroxide only lasts a few months before it becomes ineffective (aka turns to water). Unopened, it should be tossed after a year. You’ll know when it’s bad when it stops fizzing.
Insect repellent loses effectiveness after around two years from the manufacture date, which should be marked on the bottle. Don’t let the bugs win.
Like car seats, bike helmets can lose their safety effectiveness over a couple of years and after any kind of crash or trauma.
Smoke and carbon monoxide detectors can stop working after 10 years, even if the batteries are replaced.
Batteries start to expire as soon as they’re made, so the expiration date printed on them or the package is based on this and not when or how they’re used. The shelf life differs between types and sizes of battery, as well as where they are stored.
According to the Mayo Clinic, most sunscreen works at full strength for around three years.