Q. (See question 2022 above). Can someone staying in a hotel during Shabbat give the plastic card key for opening the room-door to a friend that uses that card key on Shabbat? The holder of the key uses tape on the lock of his own door, to avoid using the electronic key, since he considers using it as chilul Shabbat. However his friend argues that he knows of Rabbis that permit it. He picked up both keys before the beginning of Shabbat.
A. Horav Shlomo Miller’s Shlit’a opinion is that it is the view of most Poskim to prohibit the use of an electronic plastic-card key to open an hotel room door, and it is the accepted minhag of Shomrei Shabbos to avoid it. (See questions 749 and 1329). Therefore, one should not hand over the card key to a friend that will use it. He may be transgressing on the prohibition of Lifnei Iver or being Mesayea (helping) another to transgress a prohibition. He should live the card-key at the desk.
See question 1329 in regards to the muktza prohibition in handling the key.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a