It is a disk lock with an alarm function.
Since there is a rumor a thief is sensitive to sound, it purchases as an alarm as a lock.
In the same form, there is what has a raw material without that as right as the thing of all stainless steel.
Since the price was different only about 1000 yen, the all stainless steel which is strong to rust and has reinforcement was chosen.
If a changing battery is not practiced several times, an alarm will resound in a house (smile).