This study proposes a smart pacifier to save a dehydrated baby's life. The pacifier estimates the hydration level of the baby and notifies the caregiver (e.g. parents) of the baby the baby's total body water (TBW) and guides appropriate action through the mobile app. We designed both the hardware and the software. The hardware consists of a sensor to measure the humidity from babie's lips and a pocket for oral rehydration solution (ORS) to get a baby's body rehydrated for the first aid. In addition, the system by collecting data from app allows a hospital to know infection area by checking a dashboard. In this paper, we propose the smart pacifier and the describe the mechanism.