This paper proposes a system for quickly realizing a function for robustly detecting daily human activity events in handling objects in the real world. The system has three functions: 1) robustly measuring 3D positions of the objects, 2) quickly calibrating a system for measuring 3D positions of the objects, 3) quickly registering target activity events, and 4) robustly detecting the registered events in real time. As for 1), the system realizes robust measurement of 3D positions of the objects using an ultrasonic 3D tag system, which is a kind of a location sensor, and robust estimation algorithm known as random sample consensus (RANSAC). The paper evaluates the robustness by comparing RANSAC with a least-squares optimization method. As for 2), the system realizes quick calibration by a calibrating device having three or more ultrasonic transmitters. Quick calibration enables the system to be portable. As for 3), quick registration of target activity events is realized by a stereoscopic camera with ultrasonic 3D tags and interactive software for creating 3D shape model, creating virtual sensors based on the 3D shape model, and associating the virtual sensors with the target events. The system makes it possible to quickly create object-shaped sensors to which a new function for detecting activity events are added while maintaining the original functions of the objects.