A wearable device for detecting and/or measuring physiological information from a subject includes a housing, at least one optical emitter supported by the housing, at least one optical detector supported by the housing, a first light guide supported by the housing, a second light guide supported by the housing, a motion sensor supported by the housing, and a processor supported by the housing. The processor is configured to calculate footsteps, distinguish footsteps from heart beats, and to remove footstep motion artifacts from signals produced by the at least one optical detector. Also, the processor is configured to process signals produced by the at least one optical detector to determine subject heart rate and to produce integrity data about the subject heart rate. The process is further configured to generate a multiplexed output serial data string comprising the subject heart rate and the integrity data.