In this paper, we propose a robust packet detection algorithm for the differentially bi-orthogonal chirp-spread-spectrum (DBO-CSS). The conventional packet detection algorithms based on auto-correlation cannot avoid side band noise because of the band hopping property of the DBO-CSS. If we, therefore, use the conventional packet detection algorithms in the DBO-CSS, the performance degradation of the packet detector will break out. First, the proposed detector includes matched filters to eliminate the side band noise. Second, the proposed detector also includes auto-correlators in order to make outputs of matched filters inphase. Finally, the proposed detector gathers the energy of all sub-chirps by the summation. When we use the Permutator, the proposed detector works regardless of piconet. Simulation results show that we can detect packets in -4 dB SNR in AWGN channel and also in 0 dB in multipath channel.