The new radio-frequency (RF) transmitters have been designed to intergrate with altimeter/pressure sensor to address the research needs for bat/wildlife 3D tracking with precise alitiude (Z direction). Inside the altimeter, there is a barometric pressure sensor that measures the air pressure at the current location. The altimeter calculates the pressure difference between the reference pressure (usually the standard atmospheric pressure) and the current pressure. The greater the pressure difference, the higher the current altitude is above the reference point.