3-IN-ONE  No-Rust ShieldHonestly, this is a difficult product to review without doing a controlled experiment to determine if it is working:  if there is rust, it isn't working but if there is no rust, it may or may not be working.3-IN-ONE has a large stake in maintaining their excellent reputation--the same company also sells trusted products such as WD-40 and Lava soap.  So this is the rare situation where I would be willing to trust the manufacturer that the product works.I can say that after about a month in my toolbox, there does not appear to be new rust forming on the tools that have rusted in the past.  Average humidity here for that month is in the 60%-70% range and the storage area was not air conditioned.The product is basically a piece of sponge that holds the chemicals encased in a plastic shell that may be attached to a surface with the strip of 3M Command tape on the back.I did a great deal of research on what to me was a novel and interesting product.  Vapor Phase Corrosion Inhibitors are a tried-and-true method of preventing rust.  An excellent overview paper may be found on the website of the professional organization of corrosion engineers:  [...]The exact formulation of this product is not given by the manufacturer.  When I called their customer service number, I was referred to the MSDS which lists only polyurethane foam and "proprietary ingredients".The manufacturer recommends one unit for every two cubic feet of space.  On the manufacturer's website, the diagram in the demo slideshow showed dimensions of 2' x 2' x 2' which is eight cubic feet.  I explained this error to the very pleasant customer service representative and said that I would be checking back to see if it was corrected.  I am very pleased to report that it has since been corrected and my conclusion is that the company is responsive to consumers and is diligent about the integrity of their products and marketing.  Yes, that is impressive and all-too-rare these days.The product is activated when it is removed from the packaging so you should not open it until you are ready to use it.  (The button on front you push activates the timer only, not the product.)It is stated to last up to 90 days.  On the company's website you can sign up for an emailed replacement reminder when it is time to replace the product.  This is a clever marketing ploy but it is also very useful to the consumer.  The website is very informative and worth taking a look at if you are considering purchasing the product.  I would also not hesitate to call customer service with questions.  [...]I would recommend this product as useful for protecting valuable items prone to rust that are stored for moderate to long periods of time in small enclosed containers.  Other reviewers have pointed out that there are other methods of rust prevention that are more appropriate in other situations but it is a good product for the intended use.