In this paper, we present an idealised model of quantum cascade detectors that calculates the highest performances reachable with actual technology. It is based on an ideal vision of the electronic behavior of the transport and a Fabry–Pérot approach for the light-coupling scheme. This simple but complete picture of the device is a proficient tool to understand the detectors physics. In particular, the variation of the performances with regards to different parameters is carefully discussed and guidelines for the detector design are sketched out. This approach gives also some insight into the potentiality of quantum cascade detector technology.