In the second type of activity monitoring system,
portable sensor modules are placed on human body to
detect and record body posture signals. Noury [3]
ultilized piezoelectric accelerometer, tilt switch and
vibration sensors to construct a sensor system to detect
whether the elderly fall down or not. The sensor
signals were transmitted to a processor by using RF
wireless communication. Najafi and Aminian[4]
developed a kinematic sensor for detecting human
body posture as well as the time of walking. Mathie et
al. [5] monitored human posture using a tri-axial
accelerometer. The acceleration signals are transmitted
to a computer for processing via RF wireless
communication. Sekine and Tamura [6][7] placed an
accelerometer and a memory card on a belt for
measuring and recording the body motion. Five
postures were recognized using a wavelet transform
design. Lee and Mase[8] designed a portable sensor
module, which is composed of accelerometer and a
gyroscope for recognize sitting, standing and walking
postures. A dead-reckoning method was adopted to
determine the human position in a room. For practical
applications, however, a simple, light-weighted and
reliable posture estimation system is still a challenging
task.