A rotatable alarm clock includes a clock body received in a hemispherical socket which is attached on a base. A plurality of hemispherical covers are rotatably received in a space defined between the alarm body and the hemispherical socket. An alarm switch is installed on the alarm body. A motor is positioned in the alarm body and is capable of driving the plurality of covers to rotate via a speed-reducing gear set. When the alarm clock alarms according to a preset time, the plurality of hemispherical covers are driven by the motor to rotate to cover the alarm clock body thus preventing a user to operate the alarm switch to turn off the alarm. The user has to concentrate his/her mind to rotate the hemispherical covers back to original positions to operate the alarm switch.