Nowadays, smartwatches are increasingly used in our daily lives. Smartwatches store a large number of personal information of users and it is necessary to design appropriate ways to protect them. PIN is a widely adopted method, but it is not resistant to shoulder-surfing. This work proposes a smart-watch-based identity authentication scheme. This scheme is based on the traditional PIN authentication and prompt password entry by vibration. Three experiments have been designed to examine the performance of this method. In the first experiment, it is tested that what kind of vibration time combination is more acceptable. Results show that the vibration combination of 400 ms and 100 ms is the optimal one. In the second experiment, a set of vibration prompt scheme is designed to establish the mapping relationship between vibration and number. Results prove that the scheme can be effectively remembered and practiced. In the last experiment, the actual password input process is simulated and the traditional unlock method is compared with. Results show that inputting four digits of five-digit password can lead to an overall fast entry speed and high accuracy, while maintaining a high security. This study offers insights into identification design for smartwatches.