Abstract: Chemiluminescent materials are encased in a thin, highly frangible shell to orm a quantity of microcapsules which, when distributed evenly and in adequate concentration over a perimeter zone, detect infiltration of troops, vehicles, etc. by the chemiluminescence which results from the crushing of the shells. One distribution system uses capsules filled with a chemiluminescent material such as tetrakisdimethylaminoethylene (TMAE). When the capsules are crushed and the contents are exposed to atmospheric oxygen this material oxidizes vigorously to produce a relatively long-lasting chemiluminescence. Another two-component system utilizes capsules containing different chemical components which, when crushed and combined one with the other, produce the chemiliminescence. Both systems employ a shell formed of a film-forming coating material hardenable, into a water-soluble, air tight shell non-reactive with the active filler material.