Photoplethysmography is a non-invasive optical technique used for continuous monitoring of physiological variables such as heart rate and oxygen saturation. However, commonly used anatomical sites—such as the fingers or wrist—are prone to motion artifacts or may be inaccessible for individuals with functional limitations. This study evaluates the viability of the retroauricular region, located over the mastoid process, as an alternative site for photoplethysmography signal acquisition in comparison to the index finger. Recordings were conducted on nine healthy volunteers across five controlled physical activity stages: resting seated, standing still, dynamic squats, warm-up and cool-down. A photoplethysmography dual-channel system was developed using MAX30102 optical sensors, selected for their validated accuracy and sensitivity to red (λ = 660 nm) and infrared (λ = 880 nm) wavelengths. Each sensor was connected to an ESP32-WROOM-32 microcontroller via a TCA9548A multiplexer. Data was sampled at 100 Hz for accurate cardiovascular pulse tracking in wearable systems. Signal processing included multistage filtering, normalization, and peak detection for heart rate estimation, along with oxygen saturation calculation. Comparison between sites were based on the symmetric mean absolute percentage error and the proportion of valid time windows, defined as segments in which reliable SpO₂ estimation was achieved. Results showed high agreement under static conditions, with relative differences below 0.6% for heart rate and 0.75% for oxygen saturation. During dynamic phases, the retroauricular region maintained stable signal quality and a comparable proportion of valid windows. These findings support its use as a viable alternative for wearable biomedical monitoring technologies.