Abstract: A control target surveillance system capable of acquiring positional data of a control target in a control zone at high precision with fewer communications lines in a short period of time. A D. GPS ground station obtains differential data with respect to positional data based on a GPS signal from a GPS satellite, and sends this data to a control target to compensate the positional data obtained from the GPS signal. A surveillance cycle is time-divided by the number of SSR codes, individual time slots are associated with the SSR codes, and each control target is allowed.

Abstract: A switching device comprising a reed switch of a normal open type turned on and off by a magnetic field, a fixed bias magnet located in an area where the switch operates stably, and a starting magnet located opposite to the fixed bias magnet with the switch interposed between them and capable of applying a magnetic field, reverse to that of the fixed bias magnet, to the switch. When the starting magnet is carried close to the switch, its a magnetic field overcomes that of the fixed bias magnet to control the switching-on and -off of the switch, and when it is carried remote from the swtich, the fixed bias magnet controls the switching-on and -off of the switch.