To develop methods for supporting senior citizens is critical because the number of senior citizens is growing globally. Recently, the focus is on supporting senior citizens using information technology (IT), including the Internet of Things (IoT). In the IoT system, IoT tools such as cameras and sensors are connected and interacted by the Internet. Furthermore, we can customize their function easily using smartphones to modulate the function we want. Therefore, senior citizens should customize IoT products and help themselves. However, it is challenging to customize IoT product functions for senior citizens because they had fewer chances to use smartphones or computers than young people. Therefore, other customizing methods for IoT products are needed for senior citizens. In this study, we design a workshop to test, where the setting of the user interface (UI) is suitable for senior citizens. We develop three UIs, namely, voice, touch, and camera. To explore which method is suitable for senior citizens, we evaluate the setting time for each method. Consequently, the setting time of the voice interface is shorter than the others. Furthermore, the system usability scale (SUS) score was higher than 68, indicating that the setting method using the voice interface is acceptable for senior citizens. These results indicate that the voice interface is a suitable setting method for senior citizens.