Beyond its remarkable genome editing ability, the CRISPR/Cas9 effector has also been utilized in biosensing applications. The recent discovery of the collateral RNA cleavage activity of the Cas13a effector has sparked even greater interest in developing novel biosensing technologies for nucleic acid detection and promised significant advances in CRISPR diagnostics. Now, along with the discovery of Cas12 collateral cleavage activities on single-stranded DNA (ssDNA), several CRISPR/Cas systems have been established for detecting various targets, including bacteria, viruses, cancer mutations, and others. Based on key Cas effectors, we provide a detailed classification of CRISPR/Cas biosensing systems and propose their future utility. As the field continues to mature, CRISPR/Cas systems have the potential to become promising candidates for next-generation diagnostic biosensing platforms.