Non-disclosure agreements can be defined as an agreement by which companies or various individuals agree to keep information confidential. NDA is a contract and not a law. Contracts are interpreted in different manners depending on the state law and interpretations vary from state to state. Patent law, which is federal, is interpreted uniformly throughout the United States.
An NDA may come in handy if the same person or the company that signed the NDA goes behind your back and develops your idea. A patent, however, covers you from having your product replicated by someone else even if they innocently or coincidentally develop the same product. The individual could be held liable for a patent infringement. Filing a patent prior to disclosing any ideas to a company or individuals you do no trust will put an individual in a better position. NDA’s are only useful if the individuals are honest. This keeps honest people quiet.