Researchers at Brown University have developed a wearable sensor that uses polarized light to improve the accuracy of photoplethysmography (PPG) signals across different skin tones. Conventional pulse oximeters often underperform on darker skin due to light absorption and scattering by melanin. The new device combines two wavelengths with cross-polarized detection to reduce superficial scattering and enhance deeper vascular signals. In tests with volunteers of light, medium, and brown skin tones, cross-polarization significantly increased perfusion index—a measure of signal strength—compared to co-polarized detection. This approach could help make wearable health technologies more equitable and reliable.