The present invention is related to a cellular phone jammer permitting cellular phones to be used in an emergency, and includes a cellular phone signal-obstructing apparatus and an alarm apparatus. The cellular phone signal-obstructing apparatus further has a cellular phone signal-blocking unit, a power supply unit, and a trigger unit. The cellular phone signal-blocking unit sends out a blocking-signal to disconnect the communication between cellular phones and cellular tower within the effective range. The trigger unit connects to the power supply unit and cellular phone signal-blocking unit in series. The invention effectively disconnect the communication between the cellular phones and cellular tower within a range, yet automatically turns off the jammer when there is an emergency in the designated area to resume normal communication between cellular phones and cellular tower so that the users can call for help.
