We propose a novel two-stage non-coherent SFH/BFSK detection scheme when the environment is interfered by an uncoordinated FH system. The first stage detects user number and power level of uncoordinated FH signals. Based on knowledge of detected side information from the first stage, the second stage performs SFH/BFSK maximum likelihood detection. When user number and power level of uncoordinated FH signals are unknown, the proposed two-stage detection scheme outperforms existing multilevel FSK conventional detectors and two-user multiuser detectors. In this scenario, simulation results demonstrate a critical role of the first-stage detector in the overall scheme when it provides the above side information. On the other hand, when knowledge of uncoordinated user number and power level is available to the desired user's receiver, simulation results also show superiority of the proposed second- stage detector over equal-gain receivers and self-normalized receivers.