Hi Claudia! Great question! In many cases, these two words are synonyms, as the others have mentioned. They can both refer to an invention or tool which is for a specific purpose. However, a "gadget" is generally mechanical, while a "device" can be either mechanical or electrical. So, a smartphone is a device but is not a gadget. However, a cheese grater could be called both a device and a gadget. One thing that no one else has mentioned, however, is that "device" also has another use that is not synonymous with "gadget." It can refer to a plan or scheme, or to something intangible which is used to achieve a goal. Here is an example sentence from Google: ""writing a public letter is a traditional device for signaling dissent." In this case we see that the 'device' is not a physical object, but an action. So "device" refers to both tangible and intangible means of achieving a goal, while "gadget" only refers to mechanical devices used for achieving a goal.

We generally use "device" in reference to technology (iPhones, laptops etc.). Gadget is more commonly used to describe a small tool that really doesn't have a name (e.g. "there's this gadget that is supposed to keep the sink drain from clogging")