This paper presents a condensed design of an ultra-low-power temperature and pressure detection system based on the Highway Addressable Remote Transducer (HART) protocol. The study targets industrial scenarios in which temperature and pressure must be measured in real time under harsh conditions while maintaining low power consumption and reliable long-distance transmission. The proposed system adopts a two-wire architecture and integrates an MSP430 microcontroller, an AD7794 signal acquisition chip, an AD5700 HART modem, and an XTR115 current-loop interface. Temperature and pressure signals are sampled, digitized, processed, and then coupled to a 4–20 mA loop carrying superimposed HART digital communication. On the hardware side, the design emphasizes sensor interfacing, HART-compatible signal transmission, and current-loop integration. On the software side, it implements system monitoring, data acquisition and conversion, communication management, and CRC-based data verification. A low-power control strategy combining sleep and wake-up mechanisms is further introduced to reduce the overall energy demand of the instrument.