It going off has become a commonly used sound effect throughout the series.
It appears to be a repurposed, white foghorn and is kept on a barrel next to SpongeBob's bed. It has a light gray corner around its circular opening. It also has a red clock on the bottom of it that has a transparent blue glass screen. There is a switch behind the said clock to set the time.
In some of its appearances, it is depicted with a red snooze button.
Role in series
The alarm clock makes numerous appearances throughout the series and is typically heard going off near the start of an episode when SpongeBob wakes up in the morning. It typically blows air near SpongeBob's direction while going off and has transported him to his various destinations after he wakes up, as seen in many episodes (e.g. "Something Smells," "Missing Identity," "Life Insurance").
SpongeBob's alarm clock shows signs of sentience and nearly loses its energy, as evidenced by its coughing from a lack of oxygen due to Gary chewing on it among other things in SpongeBob's house. SpongeBob uses duct tape to fix it, but the alarm clock just falls backwards.
SpongeBob turns up the volume on his alarm clock and sets it to the waking hour in an attempt to wake Patrick from sleepwalking. The noise is so loud that it wakes several citizens up and causes worms to start barking, however it fails to cause any affect on Patrick, as he continues sleepwalking.
In some episodes, SpongeBob has to press a button on the alarm clock to stop it. In other episodes, the alarm clock stops by itself.