Terrestrial Trunked Radio (TETRA), a complex communication system based on a digital technology, is mainly used by public safety services. As the TETRA technology is included in a category of industrial goods called complex products and systems (CoPS), this communication system is the candidate CoPS example. In all business contexts, complex information technologies or information systems bring productivity gains for the organization only when the target group uses the system in the way it is supposed to be used. The underlying study investigates the factors influencing the acceptance of the TETRA technology on the end-user level. The theoretical model is based on Davis' (1989) Technology Acceptance Model. A qualitative pre-study was followed by a broad empirical assessment in quantitative terms (295 data sets). Results confirm the original TAM core constructs. When an already implemented system is examined, the behavioral intention component need not be taken into consideration in the TAM. The specific extension of the traditional TAM is especially valuable, as this study proves the high significance of the influence of perceived system interoperability. Moreover, peer group influence and competitive pressure have a significant influence on the user's attitude towards the use of TETRA technology. Social influences - except the influence from supervisors - play an important role in accepting mandated TETRA technology. The overall model provides valuable theoretical input for further technology acceptance studies and offers a better insight into the CoPS setting. (author's abstract