Until 1910 the U.S. Patent Office permitted an inventor to file an official notice regarding work in progress. Caveats were valid for one year and could be renewed from year to year upon payment of a fee. If another inventor subsequently filed an application for a similar invention, the first inventor was so notified. Although Edison filed numerous caveats during the 1870s and 1880s, there is only one extant caveat from the period 1899-1910.
The caveat, which was executed on November 27, 1907, is entitled "Cement Buildings and Process of Constructing the Same." In addition to the typed specifications, the folder contains a draft in Edison's hand; two blueprint drawings; and a published letter to the Scientific American by H. J. Le Comte, an inventor who claimed to have anticipated Edison's idea for a concrete house.