Systems and methods are provided for recording a user’s biometric features and generating an identifier representative of the user’s biometric features using mobile device such as a smartphone. The arm supports are shaped to provide a surface to resist downward force of one’s arms while allowing the arms to stay close to the body, as when holding or feeding a baby. The shadow network can include shadow network signals corresponding to signals of the asynchronous crossing. The input signal to the PMOS andor NMOS transistors may be generated by a voltage controlled oscillator circuit.