Evil waveforms (EWFs) could be considered as anomalous signals from the analog and/or digital signal generating hardware on board with imperfections or failures, and might introduce hazardous misleading information (HMI) to users. Since the first observed EWF occurrence, i.e. SVN-19 Event in 1993 , a series of techniques called signal quality monitoring (SQM) have been developed and implemented in currently running SBAS’s. Conventional SQM, represented by SQM2b, was based on multicorrelator detection techniques. However, there exist some obvious and potential limitations or disadvantages on it. To mitigate all these problems, SQM algorithms based on chip domain observables (CDOs) are emerging. The third generation of BDS has been officially declared to provide global services on positioning, navigation and timing at the end of July 2020, while BDSBAS is under development, aiming at providing DFMC SBAS services under realistic requirement of high inter-operability. This paper proposes an SQM algorithm based on CDOs, to explore the effectiveness of chip-shape detection technique for normalized DFMC SBAS SQM on BOC signals. Detailed descriptions of the proposed algorithm and evaluation scheme with CDOs obtention, thresholds derivation and process of detection are expounded. In addition, simulations on BDS B1C signal (BOC(1,1) modulated) are carried out, and analyses on varies aspects are presented for confirmation of correctness and validity.