To provide a system capable of accurately sensing the position of a wanderer such as a wandering aged person, a sensing system efficiently utilizing the good will of registered donor and further, a system grasping the information of all ID information registrants.

This sensing system is for registrants such as the above object person and is provided with a transmitter and a receiver. The receiver is arranged at a position that can be recognized by a manager, the transmitter is provided with at least an antenna and an IC package, ID information is recorded on the IC package and the IC information can be transmitted. The transmitter is attached inside the mouth so that these object persons can easily and willfully remove the transmitter. In the case of an ID information registrant, the transmitter does not have to be carried as a card, etc., because the ID information is carried in the mouth, and when the registrant approaches a sensor, the ID information in the mouth enables the registrant himself/herself to be discriminated so that the system can be replaced for various cards etc.