Devices, systems, and methods using wearable time domain-based activity tracker

A wearable optical measurement device configured to be worn on an appendage of a user, the wearable optical measurement device comprising:

• a light source configured to emit light pulses directed at the appendage;
• a detector configured to detect arrival times for photons of the light pulses after the photons are scattered by tissue within the appendage;
• a housing configured to house the light source and the detector;
• and
• a processing unit configured to:
• generate, based on the arrival times of the photons at the detector, histogram data associated with the appendage;
• determine, based on the histogram data, an absolute optical property associated with the appendage;
• determine, based on the absolute optical property, a blood oxygenation level of the user;
• determine, based on the histogram data, at least one of a respiratory rate of the user, a heart rate of the user, or a heart rate variability of the user;
• access inertial measurement unit (IMU) data associated with the user;
• and
• determine, based on the IMU data, and the at least one of the heart rate, the heart rate variability, or the respiratory rate, a sleep stage of the user.

A wearable optical measurement device configured to be worn on a wrist of a user, the wearable optical measurement device comprising:

• a light source configured to emit light directed at the wrist;
• a detector configured to detect arrival times for photons of the light after the photons are scattered by tissue within the wrist;
• a housing configured to house the light source, the detector, and a processing unit;
• a strap coupled to the housing and configured to hold the housing against the wrist;
• and
• the processing unit configured to:
• generate, based on the arrival times of the photons at the detector, histogram data associated with the wrist;
• determine, based on the histogram data, an absolute optical property associated with the wrist;
• determine, based on the absolute optical property, a blood oxygenation level of the user;
• determine, based on the histogram data, at least one of a respiratory rate of the user, a heart rate of the user, or a heart rate variability of the user;
• access inertial measurement unit (IMU) data associated with the user;
• and
• determine, based on the IMU data, and the at least one of the heart rate, the heart rate variability, or the respiratory rate, a sleep stage of the user.