With the rapid development of wearable technologies, wearable devices are gradually entering people's daily life. As a novel way of human-computer interaction, wearable devices have brought more and more convenience and assistance to people than ever before. In this paper, we firstly make a classification of wearable devices based on their functions and how they are worn. An introduction to the current development of wearable devices is also presented. Then, the challenges in the area of wearable devices and their possible solutions are discussed. Finally, the conclusions are drawn on the development and future trends of wearable devices and technologies.