Wearing a key belt on Shabbos: does the belt need to have a purpose? I.e. if worn on a jacket should the buttons be left open? Can it be worn simply over a shirt? With 2 belts the poskim seem to say that the reason behind the Remo that prohibits, is because the second belt has no purpose since there is already one belt… which would imply that the first belt must also have a purpose, hence a Shabbos gartel to carry a key would not be allowed to be worn simply over a shirt or a jacket with closed buttons. A reply is much appreciated, possibly with sources. Thank you.
The belt does need to serve some purpose, the most basic and simple being actually holding up one’s pants, like a regular belt.
If the belt merely hangs loosely over one’s clothing, it becomes clear that the belt is nothing more that a ruse for carrying the key, and this is a problem, for the entire permission for carrying the key is that it is part of an “authentic” belt. In the words of the Aruch Ha-Shulchan, one must carry it out “with the intention of a belt.”
The most convenient form of belt for achieving this is elastic, ensuring that it is more or less the right fit.