This study was conducted to quantify the response characteristics of a smoke detector. The theory on the entrance resistance of a smoke detector was reviewed, and a method for quantifying the response characteristics through the time constant and characteristic length was proposed. To apply the proposed method, a real-scale fire test of paper and wood, as described in the Excellent Quality Certification Test Rules for Detectors, was conducted. The time constant of the smoke detector was classified into three categories and derived. For domestic smoke detectors, the time constant can be reasonably determined based on the smoke peak value in fires that generate grayish white smoke. This study can serve as a reference for further studies on various samples and fire patterns; the expected response characteristics can be inferred when the detector is installed, which will contribute to improving the reliability of the detector.