If you do a search yourself, and unless you find exactly the same invention as yours and know you're out, a patent agent should be consulted to help analyse the search results. This is because a patent office Examiner usually combines two or more references to find that an invention is obvious and thus non-inventive - the validity of such a finding often being less than clear to the inventor.

Typically a patent search will include examining Canadian and foreign patent databases for related inventions, as well as an Internet search. Searches should also include looking at any public sale or use of a similar device or process by others.

Searches are also just good practice and can save you unnecessary marketing and other patent expenses later. If a search reveals that you do not have an invention, you are less likely to expense the patent costs, and save even greater costs at the marketing and development stage.

If a patent or technology exists which classifies as prior art, you cannot obtain a patent, even if the patent is expired. Once patented or available to the public, it cannot be patented again, unless you have a significant, unobvious improvement.

A search which finds pertinent prior art discourages most inventors, however, they may still be able to buy the already existing patent, or negotiate a license to make, use or sell the invention. If the prior art is an expired patent, anyone is free to make, use and sell it - you just do not get a monopoly.