Multisensor-based fire alarm systems have been developed as an automatic fire detection technology. However, only two or three fire signatures do not suffice to recognize a fire. Conventional fire detectors must touch sufficient targets (heat or smoke) so that they respond slowly to the alarm. This article proposes several approaches that use the radiation-sensing technologies to detect fire behaviors. Four features, temperature, hot CO2 gas, flicker, and the UV energy of the flame are adopted in the system to analyze the fire traits. Four kinds of sensors and one IR transducer are used successfully to evaluate these features. Experimental results show that the use of two pyroelectric sensors can accurately “see” the appearance of combustion by detecting the CO2 emission instead of the particle density of smoke. The combination of a blue and an UV sensor is used effectively to pickup the UV component of the flame. The information is presented on a personal computer using LABVIEW software and a data-acquisition interface. Although this article focuses on techniques for measuring IR and UV energies, in off-line work, a trained back-propagation network verifies that the measuring system is effective in collecting the information on fire behaviors. Results of this study provide a valuable reference for designers in developing a novel fire detector.