Open the package and rotate the lock beam by 180°. When you hear the sound, the alarm mode is on. In this mode, if an external force touches the lock body, the lock body emits a sharp and harsh alarm sound. Reverse the lock beam 180° again, there is no “di” sound prompt, normal mode is on. No alarm will sound in this mode. Each hand is given a replacement battery. This alarm clock has a built-in siren that triggers an alarm that emits up to 110 decibels of loud sound when locked or shaken, making it ideal for avoiding theft.