A patent caveat is a legal instrument or document that was filed with the U.S. Patent Office (PTO). They are similar to the provisional applications filed today. Such caveats were introduced by the US Patent Act of 1836. The Act provided that: any citizen of the U.S., or an alien who resided in the U.S. one year next preceding, and who has made oath of his/her intention to become a citizen of the U.S.; and who invented any new art, machine, or improvement can file a caveat in the PTO making a request to protect the invention till the person has matured with the invention. A fee was also associated with such caveats. However, the fees were much less than the fee that has to be paid along with a patent application. Such caveat were filed in the confidential archives of the PTO, and preserved in secrecy. However, patent caveats were discontinued in 1909.
A patent caveat was similar to a patent application. It contained the description, design, and drawings of an invention, but the applicant did not make any claims through such caveats. Patent caveat was just an official notice of intention to file a patent application at a future date. Caveats expire after one year. However, they can be renewed by paying an annual renewal fee.
The purpose of a patent caveat was to protect the invention for which the caveat was filed, and to prevent the issuing of a rival patent for the same invention to a subsequent inventor. Before issuing a patent, the caveats filed within the preceding year were searched. And, if a patent application was made for an invention for which a caveat had been filed, the Commissioner had to give notice, by mail, to the person who filed the caveat. The caveat holder was given three months time to take benefit of his caveat and file the formal patent application for the invention.