This paper introduces a novel way to enable users to create temporal smart surroundings easily at open-air events. The final goal of this research was to support social activities in public spaces, such as festivals, camps, and outdoor-ceremonies with ubiquitous computing technologies. We designed and developed universal modular units called "I/O-CRATEs", which are box-shaped units embedded with microcomputers, sensors, actuators, and batteries. We demonstrated the possibilities of our units with a one-night special event. Through this practical experience, we found "I/O- CRATEs" could easily be used to create smart and enjoyable surroundings in many places.