Abstract: An alarm transmission system with portable receivers for watching a site, which system comprises a plurality of portable and removable autonomous detection units, a plurality of portable autonomous receiving modules capable of releasing signalling or warning means incorporated to the said receiving modules upon receipt of signals sent by a transmission unit and a central information-receiving and processing unit equipped with at least one receiving module, and in which system the signal transmission unit is constituted on the one hand by radio-transmission and coding means associated to each detection unit and on the other hand by means of reception by radio-link and decoding means incorporated to each portable receiving module.