With the advent of highly complex and dense modern CMOS circuits, defects caused by parametric and process variations, e.g., are more and more difficult to detect. Many hard-To-detect defects not sensitized through the critical paths can easily escape from the conventional testing methods. In order to reduce the product defect level, we introduce the notion of quorum sensing (QS) to circuit testing (sensing) for improving the quality and reliability. The proposed thermal quorum sensing (TQS) mechanism triggers a thermal chain reaction to expose the subtle variations in the circuit due to small defects, which can be observed by the common cell population behavior. A model is introduced to charactize the feature of TQS on circuit. The simualtion result verified by the ISCAS s9234 benchmark with 45nm CMOS standard cell library shows when the number of small defects injected is more than 489, the difference in total current will be higher than 2.08mA. It can discover the subtle faults compared with other state-of-The-Art or traditional testing methods.