From the Super Mario Wiki
Alarm Bob-ombs are a species of Bob-omb enemies found in conjunction with sleeping Naplocks during the events of Mario & Luigi: Bowser's Inside Story. They resemble small black and gold alarm clocks. Their only form of attack is to dash back and forth across the screen in front of the player making an irritating beeping noise; in order to counter them, Bowser must punch with good timing to hit them and end the attack (if he does not, an accompanying sleeping Naplock will reach out and hit the Alarm Bob-omb on the top of its head to turn it off, canceling the attack). If Bowser chooses to swallow them with his vacuum attack, Mario and Luigi must do the same thing with their hammers. However, inside Bowser, there is no Naplock to turn the Bob-omb off, and if they take too long, the enemy will begin to flash bright red, ring loudly, and eventually explode, damaging one of the Bros. and possibly causing the Dizzy status. If an Alarm Bob-omb is destroyed outside of Bowser, any sleeping Naplocks will wake up.
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