A portable alarm system designed for unoccupied unsecured locations, such as construction sites, machinery, campsites and the like. The alarm system defines a continuous monitoring line about the perimeter of the unsecured location using a plurality of wireless sensors attached to a flexible non-stretchable tape suspended between to vertical poles. The system has motion-sensing/detecting capabilities such that any movement of a housing where the microprocessor of the system is located generates audible/visual alarm. Each of the wireless sensors has a magnet and a transmitter positionable within a predetermined distance from the magnet. If the intruder tampers with the tape and increases the distance between the magnet the transmitter, the alarm is activated as well.