A low-power low-voltage system on a chip (SoC) was designed and implemented in a 0.18-$\mu$m CMOS process to provide a fully integrated sensor node solution for wearable wireless health monitoring. The SoC contains a sensor interface circuit, an analog-to-digital converter, a digital signal processor and a radio-frequency transmitter. Only a minimal number of off-chip components, which include an antenna, a crystal and supply decoupling capacitors, are used for improved user experience and affordability. The sensor node developed was demonstrated together with the prototype personal server. The acquired electrocardiogram (ECG) signal could be reliably transmitted to and monitored by the personal server over a distance greater than 5$~$ m. The SoC consumes only 700 $\mu$W at 0.7-V supply voltage when it acquires ECG signal from the patient and transmits it through the 433.92-MHz channel with an output power of ${-}$ 16 dBm. This low-power sensor node solution enables continuous and real-time health monitoring for more than 200 hours without changing the battery, when a typical button-cell battery (e.g., CR2032) is used.