Q. (Re- prior question 1328) What is HoRav Miller’s opinion in regards to the card being muktza because it is a utensil dedicated to a prohibited task and then you would be permitted to carry it with you in the hotel and give it to a staff member to open the door. Or maybe is it muktza because of fear of monetary loss, as quoted in your answer, and then you would have to live the card at the front-desk?

A. Horav Shlomo Miller’s Shlit’a disagrees with opinion of the Melochim Om’nayich that rules a key-card to be muktze machmas chisaron kis. He maintains it is only a case of machmas issur, or by dint of the prohibition that is inherent in its normal use.
In principle, this type of muktze is permitted when the object could be used in a permitted way (letzorech guffoi), or when the space it occupies is needed for another permitted use (letzorech mekomo). However, he maintains that the use of the card by the Gentile to open the door at your request, as mentioned in question 1327, does not constitute letzorech guffoi, since you cannot open the door yourself. Therefore, the card should remain at the front-desk, from where the attendant can take it.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a