Disclosed is an apparatus which, even when it becomes impossible to take an image of a mobile object due to existence of an obstacle to hide the mobile object, is capable of making a simulatory screen display of the mobile object, thereby notifying a driver of a risk of collision with the mobile object. By applying focused and unfocused stimulation to the electrode array and comparing the difference in the responses to the two types of stimulation the interaction may be determined. The RFID tag may be comprised in a non-removable item worn by the wearer, such as a bracelet. The first and second intermediate signals have a phase difference of 180\xb0 from each other. In another aspect, the invention provides a dynamic scheduling method.