A long-range transmission demonstrator for low data rate environmental sensor networks is under development. It uses the ISM free-access frequency band at 433 MHz. In addition to distance attenuation, a major issue is the presence of numerous radio frequency interferences in this band. With a view to optimizing the sensor life and cost, the system complexity has been shifted to the central station which will be based on array processing techniques. In this paper, we describe a spatial cyclostationary detector for triggering the acquisition of sensor data frames in this highly corruptive radio environment.