Abstract: Methodology and circuitry for determining if a device, such as a cellular phone or personal digital assistant has been tapped is disclosed. The device includes an accelerometer and in response to an acceleration, the accelerometer outputs an acceleration signal. The accelerometer may continuously output an acceleration signal even if no acceleration occurs. A tap detection device receives the temporally sampled acceleration signal and takes the first derivative of the temporally sampled acceleration signal producing one or more derivative values. The tap detection system compares each derivative value to a threshold value and if the derivative value exceeds the threshold a tap is detected. By taking the derivative of the acceleration signal, the noise floor for the acceleration signal is reduced leading to more accurate results with less false positives and less positive negatives.

Abstract: Methodology and circuitry for determining if a device, such as a cellular phone or personal digital assistant has been tapped is disclosed. The device includes an accelerometer and in response to an acceleration, the accelerometer outputs an acceleration signal. The accelerometer may continuously output an acceleration signal even if no acceleration occurs. A tap detection device receives the temporally sampled acceleration signal and takes the first derivative of the temporally sampled acceleration signal producing one or more derivative values. The tap detection system compares each derivative value to a threshold value and if the derivative value exceeds the threshold a tap is detected. By taking the derivative of the acceleration signal, the noise floor for the acceleration signal is reduced leading to more accurate results with less false positives and less positive negatives.