This paper describes a prototype of a metabolic monitor designed for field work in biological anthropology, human ecology, and bioengineering. Such applications require robustness, reliability, easy replacement and low costs of usage and technical support. The purpose of this system is to monitor the resting energy expenditure (REE) and during physical activity, using the method of indirect calorimetry from expired CO2 measurement and estimation of O2 consumed. In the design and construction of the system have been used low-cost industrial sensors. The system performs continuous measurement of the pressure generated in the mouth and the CO2 produced during physical activity and stores this information on a removable flash memory. Results of validation using one standard equipment with certified traceability are presented