Privacy-preserving social interaction measurement

A wearable device, comprising:

• a housing;
• an attachment mechanism, attached with the housing, that permits the wearable device to be worn by a wearer;
• a microphone housed by the housing;
• a photoplethysmography (PPG) sensor, housed by the housing;
• and
• a processing system comprising at least one processor, communicatively coupled with the microphone and housed by the housing, wherein the processing system is configured to:
• receive an audio signal from the microphone;
• receive a PPG signal from the PPG sensor;
• process the audio signal using an audio-based machine learning model stored by the processing system, wherein the audio-based machine learning model is trained to detect a presence of speech;
• process the PPG signal received from the PPG sensor using a PPG-based machine learning model stored by the processing system;
• using a first output of the audio-based machine learning model and a second output of the PPG-based machine learning model, determine whether the audio signal comprises speech spoken by the wearer of the wearable device;
• output an indication of whether speech spoken by the wearer is present within the audio signal based at least in part on processing the audio signal using the audio-based machine learning model;
• and
• discard the audio signal such that the audio signal is not stored after the indication of whether speech is present is output.