An alarm device for a notebook, including a housing, a circuit board, a press key module, a sensing unit and an alarm unit. The housing is a flat housing. A bottom face of the housing is attachable to a surface of the notebook. An upper section of the housing is formed with an arced edge. The press key module is arranged on the surface of the housing for a user to operate to generate control signals. The circuit board, the sensing unit and the alarm unit are arranged in the housing. The sensing unit serves to sense respective tilting or vibration states and output a sensing signal to the circuit board. The circuit board includes various related electronic components and a rechargeable battery for supplying power for the circuit board. The circuit board serves to accept the control signals from the press key module and the sensing signals from the sensing unit and output an alarm signal to the alarm unit. The alarm unit serves to accept the alarm signal from the circuit board to produce alarm sound/light.