Answer:
I can be found in seconds, minutes and centuries, but not in days, years or decades.
Securing your documents is easy with these trusty metal objects
This is a dead giveaway
What has no hands but might knock on your door, and if it does you better open up?
As strong as love, more dangerous than cancer.
Though not a plant, has leaves. Though not a beast, has spine. Though many wouldn't need this thing, It's more valuable than wine.