A bulk-doped semiconductor that is at least one of the following: a single crystal, an elongated and bulk-doped semiconductor that, at any point along its longitudinal axis, has a largest cross-sectional dimension less than 500 nanometers, and a free-standing and bulk-doped semiconductor with at least one portion having a smallest width of less than 500 nanometers. as removeably attachable or as a permanent system that comes with said luggage or backpack. This allows the user to visualise the location of each user, without having to manually determine the position of each user.