Flares have an average lifespan of between 3-5 years.
After that the propellant starts to degrade, meaning that you risk your expired flare not firing at all when you need it.
The expiry date should be printed on each flare. If you can't read the expiry date or the flare shows signs of age (eg. rust around any metal parts, worn labels) replace them anyway. Read more about flares.
EPIRB or PLB
Battery needs to be replaced by the expiry date.
The long-life, non-rechargeable battery on your EPIRB (emergency position-indicating radio beacon) or PLB (personal locator beacon) is usually guaranteed to last at least five years, and often as much as ten.
Check the expiry date listed on the side of the beacon, to ensure the batteries are still within their use dates. Give it a test every so often using the manufacturer’s guidelines - there should be a test button which won't transmit a signal, so you know the beacon is still working correctly.