In this paper, we proposed an infant monitoring system to reduce the potential risks for Sudden Infant Death Syndrome (SIDS). This system can be used for infants at home or in a hospital nursery room. The system consists of carbon dioxide (CO 2 ) sensors and active Radio Frequency Identification (RFID) technology. A commercial metal-oxide based CO 2 sensor was chosen and characterized in sensitivity, selectivity and humidity dependence. A proof-of-concept system, to be used for two infants in the same room, was designed and assembled. The RFID transmission was accomplished with a wireless module at two different operating frequencies. The results are promising. A method for further practical applications in a large nursery room is also discussed in details in this paper.