Embodiments relate generally to electrical and electronic hardware, computer software, wired and wireless network communications, and wearable computing devices for sensing health and wellness-related information. More specifically, disclosed is a physiological sensor using, for example, acoustic signal energy to determine physiological characteristics, such as a heart rate, the physiological sensor being disposed in a wearable device (or carried device). In one embodiment, a physiological signal generator is disposed substantially in a wearable housing. At least a portion of a skin surface microphone (“SSM”) including a piezoelectric sensor is configured to receive acoustic signals. The wearable housing is configured to position the SSM to receive an acoustic signal originating from human tissue. The physiological signal generator is configured to receive a piezoelectric signal based on an acoustic signal, and to generate a physiological signal including data representing a heartbeat or heart rate.
