Abstract: We describe a medical device, in embodiments a battlefield triage device, configured to be attached to and carried by a person. The device comprises a sensor module to attach to a person's face. The module having a respiratory sensing region comprising an air temperature sensor and a humidity sensor arranged such that, when the module is attached, airflow in and out of the person's lungs flows over said respiratory sensing region. The device also includes a signal processing system, coupled to the sensor module, to process and combine signals from the temperature sensor and from the humidity sensor to determine a respiration rate for the person and a system to output data indicating the respiration rate. The sensor is arranged to attach to/over the person's nose and/or mouth such that airflow in and out of the person's lungs, in particular, via the nostrils flows over the respiratory sensing region.