The strips do work, They do need changing but that does depend on how often you open whatever it's airtight in. A friend smokes in one room in his house and he had some coins he had just sitting there on the table and In a short time they toned on one side almost gold in colour, I should have taken a pic and I have 3 handing coins myself. that been out for 2 years now, handled every day and they nowhere near as toned. so the environment does have a lot to do with it as well. smoking must add more sulphur to the air as thats what really makes the coins tone. The strips as far as i know remove the sulphur. so I think if it's sealed and you don't open for years should be as new.