The security and privacy of the Android system is an important research area due to the widespread use of Android devices. Most of the existing researches on this area focus on the mobile and wireless networks. Security breach through the speaker remains relatively less explored. In this work, we focus on potential security breaches in the Android system using ultrasonic channel in the speaker. We have proposed a dynamic vocabulary selection strategy to facilitate faster data transmission in ultrasonic side-channel attacks. We also propose a novel piecewise linear amplitude reduction technique that helps the system to achieve a higher bit-rate and higher amplitude for a long time. Our proposed system improves the bit-rate of the modulated audio by 27.5% and maximum attack distance by 20%. The improvement for the data transfer rate is 155% for numeric data, 70% for alpha-numeric data and 27.5% for any ASCII character. We also propose a detection mechanism for similar attacks using Android log analysis.