Abstract: A reed switch-based burglar alarm features two reed switches mounted perpendicularly to each other within the alarm enclosure. The orientations of the perpendicular reed switches permit the enclosure to be mounted in alternate ways with respect to a movable structure being monitored. The first reed switch lies in a plane parallel to the surface to which the alarm is mounted, and the second reed switch lies in a plane perpendicular to the mounting surface. Thus, a magnet can be mounted on a swing-out type door and the enclosure mounted on a wall adjacent to the door such that the magnet actuates the first reed switch when the door is closed. Similarly, a magnet can be mounted on a roll-up type door and the enclosure mounted to a surface perpendicular to the door such that the magnet actuates the second reed switch when the door is closed. The alarm preferably includes features which enable it to be mounted on the outside of the space being protected.