Multiband orthogonal frequency-division multiplexing (MB-OFDM) systems employ frequency-hopping technology to achieve the capabilities of multiple access and frequency diversity. However, they also complicate packet detector (PD) in terms of the requirement for the high hardware complexity. In this paper, we propose several low-cost design schemes for the PD, such as Walsh-Hadamard decomposition, buffered summation, and sign-bit-remaining methods. The estimated gate count of the resulting implemented PD is less than half that of existing solutions.