The invention provides a fall alarm, a fall alarm detector and a fall alarm detecting method. The fall alarm comprises an MCU (microcontroller unit), a sensor unit, a GSM (global system for mobile communications) wireless unit, a display unit, a push-button unit, an alarm unit and a Bluetooth unit. The sensor unit, the GSM wireless unit, the display unit, the push-button unit, the alarm unit and the Bluetooth unit are connected with the MCU. The sensor unit comprises a 3D (three-dimensional) acceleration sensor for detecting the acceleration of a user and an air pressure sensor for detecting air pressure data. Through the data acquired by the 3D acceleration sensor and the air pressure sensor, the moving-down state, state of weightlessness and collision state of the body center of gravity of the user can be detected accurately, and misjudgement is less easy to occur. When the user is judged to fall down, the fall alarm operates timely, and accordingly injuries of unattended patients or old people can be reduced to the lowest level.