This paper presents a wireless and wearable body-pressure-monitoring system for the on-site, real-time prevention of pressure injuries for immobilized patients. For the prevention of pressure-induced skin injuries, a wearable pressure sensor system is designed to monitor the pressure at multiple sites on the skin and to alert the danger of prolonged application of pressure on the skin with a pressure-time integral (PTI) algorithm. The wearable sensor unit is developed using a pressure sensor based on a liquid metal microchannel and integrated with a flexible printed circuit board that includes a thermistor-type temperature sensor. The wearable sensor unit array is connected to the readout system board for the transmission of measured signals to a mobile device or PC via Bluetooth communication. We evaluate the pressure-sensing performances of the sensor unit and the feasibility of the wireless and wearable body-pressure-monitoring system through an indoor test and a preliminary clinical test at the hospital. It is shown that the presented pressure sensor has high-quality performance with excellent sensitivity to detect both high and low pressure. The proposed system measures the pressure at bony sites on the skin for about six hours continuously without any disconnection or failure, and the PTI-based alarming system operates successfully in the clinical setup. The system measures the pressure applied to the patient and provides meaningful information from the measured data for early diagnosis and prevention of bedsores to doctors, nurses, and healthcare workers.