The disclosed embodiments provide a head-mounted device. The head-mounted device includes a sensing apparatus, which contains a first infrared emitter and a second infrared emitter positioned below the first infrared emitter, wherein the first and second infrared emitters alternate emission of infrared pulses at an eye of a user. The sensing apparatus also includes a first infrared detector that produces a first measurement of a reflection of the infrared pulses from the eye of the user. The head-mounted device also includes a processing apparatus that analyzes the first measurement from the first infrared detector to characterize an eyelid movement of the user.
