An improved magnetic switch (10) is provided which is designed for use in an alarm circuit (52) in order to detect relative movement between first and second members such as a door (14) and frame (12), so as to signal unauthorized opening of the door (14). The switch (10) includes a switch assembly for mounting in frame (12) and having first and second switch elements (40,42), a permanently magnetized, shiftable body (44) adjacent the elements (40,42), and a first attractive component (36). Additionally, the switch (10) has a second attractive component (22) for mounting to the door (14), which is in the form of a ferromagnetic component such as a permanent magnet (50) or steel plate (60). In use when door (14) is closed and circuit (52) is armed, the magnetic attraction between body (44) and component (22) shifts the body (44) to a switch-closed position in simultaneous contact with the switch elements (40, 42). If the door (14) is opened, the magnetic attraction between body (44) and component (36) moves the body to a switch-open position out of simultaneous contact with the switch elements (40,42), thus triggering circuit (52). If an intruder attempts to defeat the switch (10) through an external magnet (58), this again moves the body (44) to a switch-open position, triggering the circuit (52).