To in bombardment of a building (12) such as a persons not always all operating there field camp or a arsenal (19) to send to warn therewith in shelters and stop (31), but only to persons (19, 2), the currently within the equipped endangerment zone (20) with respect to an expected point of impact (17), are the persons (19) with GPS-based alarm devices (24) to receive prediction data of an impending impact point (17) and determine their impact distance (21) thereof. If, at the current location (25, 2) a person (19, 2) whose impact distance (21, 2) is smaller, by the adjacent edge of the than the endangerment zone (20) given minimum safety distance (22, 2), the signal transmitter is driven (26) of the warning device (14) and on the display (27) displayed, in which alignment direction (28)-taking into account about of adjacent obstacles (30) and the position of the working space next-richable (31)-this person stays (19, 2) should settle out. Persons (19, 1), avoids endangerment zone the outside the need (20) reside, are not warned, not because they adjust their current activity, what burdensome panic situations in the building (12).