➜ You cannot simply see if something has been patented, you must make sure that the item has not been patented. This means that you must examine each patent in your subject area to determine if there is prior claim to your idea(s).
➜ You must search as far back in time as your invention has been technologically possible.
Utility patents have a life span of 20 years. Anything previously patented cannot be re-patented, even though that patent may have expired. Once a patent expires, the invention becomes part of the public domain, meaning that anyone may be able to use or manufacture the invention.
First, determine your invention's classification(s); then examine the patents in each classification and compare them to your invention. You may also want to search for non-US patents.
Most patent databases are web based. You must search as far back in time as it was technologically possible for your invention to exist. While web databases are useful for preliminary searches, complete searches may require a visit to a U.S. Patent Office Search Facility.
After searching the patent literature, also look at the non-patent literature. Sometimes new ideas are published in professional journals or presented at conferences before a patent is granted, or even if a patent is not pursued. SciFinder Scholar indexes chemical patents from approximately 25 countries and patent organizations. It also issues a patent concordance, listing patent number by issuing country and the corresponding patent number in other countries.