This result is expected. This is not because of the MAX30101/2, but rather because of the PPG signal itself. Colder temperatures reduce blood flow, which results in a reduced PPG signal quality. This affects our algorithm’s ability to detect heart rate and SpO2. I would recommend looking at this research paper if you would like to learn more about this topic: https://www.sciencedirect.com/science/article/pii/S2405896315020571