Disasters create mass casualties and the number of casualties usually surpasses the capability of medical resources, hence, medical teams must attach paper triage to casualties for determining the priority of treatments based on the severity of their condition. However, since casualties' condition could change at anytime, the paper triage cannot provide the latest information of their health condition. Therefore, we have developed a wearable medical device that can continuously monitor the health condition of casualties. It is a lightweight and low-cost wearable electronic triage with sensing system that can monitor the vital sign of casualties and classify them into three levels of severe conditions, i.e., major, delayed, and minor status. The electronic triage is mainly built from a low-power 8-bit microcontroller unit, RF units, and sensors including pulse oximetry and thermocouple breath sensor. This electronic triage has been developed using low-cost electronic components that are available in developing countries such as Indonesia, so that, our electronic triage can be easily manufactured and maintained locally. Furthermore, we have also developed a simple android-based mobile application for data acquisition, priority classification, data storage and data transfer to medical record server in hospitals.