In this work, we describe the design and construction of a pulse oximeter for remote patient monitoring. The proposed device uses the ESP8266 microcontroller as the core component to establish the wireless connection and send information to a node.js server. Then, a web service shows the saturation of oxygen and the heart rate through a WebSocket connection. This paper describes the hardware and software designs, justifying the decision to select each component of the proposed device. Finally, some experimental results are shown to illustrate the performance of the developed prototype.