| 摘要 |
PROBLEM TO BE SOLVED: To detect a single person, who may be near by, by using a simple method even without user's manual on hand under jam conditions of a crowd or the like and to get contact with the single person in some cases. SOLUTION: This invention relates to a first type wrist watch, which comprises a receiver that is a narrow band receiver connected to an antenna for 433 MHz industrial frequency band and able to satisfactorily receive and amplify at least two discrete frequencies f1 and f2 separately, a low output optical display area of an LCD, a light emitting diode or the like, and an explanatory note for explaining the meaning related to optical display area, and to a second type wrist watch, which transmits the discrete frequencies f1 and f2 by using a transmitter SA, where the electric fields of the discrete frequencies propagate up to about 10 m away into free space with respect to the sensitivity of receiver (EB) of the first type wrist watch. |
