Device is something invented to accomplish a specific purpose or to provide certain results.
Devise is a verb meaning to invent or to contrive: “It must be possible to devise some way to protect the country from corruption.”
She wanted to devise a device that would make driving safer and less expensive.
Always remember, device, the noun, is spelled with a c. Devise is a verb. A bottle-opener is a device. And you devise a plan for killing someone or even making a fool of your boss. The exception to this rule is the usage of the word devise as a noun, where it refers to a legal term, meaning the willing of real property.