Abstract: An alarm device for a mobile phone includes a receiver for receiving a signal transmitted from a transmitter of a mobile phone only if the receiver is located within a predetermined distance from the mobile phone, an alarm unit for generating an alarm signal, a timing circuit for measuring a predetermined time duration and triggering the alarm unit upon elapse of the predetermined time duration, and a microprocessor for prestoring a subscriber identification module number therein, checking if the mobile phone identification number contained in the signal received by the receiver is identical with the prestored subscriber identification module number, and resetting the predetermined time duration of the timing circuit if the mobile phone identification number contained in the signal received by the receiver is identical with the prestored subscriber identification module number.