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Some companies have begun making felt tip pens that can detect counterfeit bills. Draw a line or an "x" on suspicious bill to see if it leaves a mark, which can indicate a counterfeit bill. Be aware that detector pens are not foolproof, but work in many cases because their active ingredient, which is an iodine solution, reacts with wood-based paper. Realize that a detector pen may leave a pastel mark on an authentic bill and that it will fade within a day. This can help you identify which bills you've checked. Purchase counterfeit detector pens at most large retailers or office supply stores. They generally cost around $5 and can check up to 3,000 bills. If you work with a lot of notes, you may want to consider getting a machine that detects counterfeit bills. Running bills through these machines can help you ensure the authenticity of your money in a quick and effective manner. Recognize that there is a wide variety of counterfeit detecting machines a broad range of price points. Buy the type of machine according to the type of work for which you need it. Machines can do everything from detecting watermarks and other features with UV-light to detecting magnetic strips and magnifying micro-printing feature. Place a stack of bills into the machine and it will self-feed and alert you if it discovers Buy your machine at a large retailer or office supply store. You can ask other businesses or colleagues if they have any suggestions on good models. Most notes in circulation have features, such as watermarks or security threads, that are visible when viewed under ultraviolet light. If you work with large sums of cash or prefer to not mark bills, consider getting a UV-light to scan for counterfeit notes. Choose a model appropriate to your needs. You may want to consider self-feed scanners or hand-held UV-lights that illuminate security features. You can buy UV scanners at many large retailers and office supply stores. If you are truly unsure if a note is authentic after looking at it or scanning it, take it to your local bank. Most banks have personnel and devices that can see if the notes are counterfeit. Explain to the bank manager that you are concerned money you received is counterfeit but are not sure how to tell. Ask if the branch can verify the money and then follow any suggestions the staff has if they discover fake notes. Remember to be kind and provide any information you can about the origin of the notes.
Mark the note with a detector pen. Run notes through a detector machine. Scan notes under UV-light. Go to your local bank.