Method and apparatus for monitoring present location of a site arrestee confined to a permitted site of arbitrary size. Present location of the arrestee can be checked at selected time intervals of several hundred milliseconds to thousands of seconds, as desired. The arrestee wears a location-determining ("LD") unit that receives electromagnetic signals that contain information allowing determination of the present location of the LD unit and arrestee, from three or more non-collinear signal sources. These sources may be radiowave subcarrier transmitters, or may be a combination of radiowave subcarrier transmitters and (1) transmitters for a Loran, Omega, Decca, Tacan, JTIDS Relnav or PLRS or similar ground-based system, or (2) transmitters for a satellite-based positioning system, such as GPS or GLONASS. Present location or change in present location of the LD unit is determined and compared with the permitted site boundary at selected times to determine if the arrestee is present at the site. The LD unit issues an alarm signal if the arrestee is not on the presently defined site. The permitted site can be redefined, for a selected time interval, to include the first designated site, a second designated site and a corridor extending between the first and second designated sites. This allows the arrestee to temporarily leave the original designated site to seek service for medical or other needs, or to be transferred to another site. The arrestee can be excluded from one or more designated exclusion sites.