I was just on the Allure a week ago. The sliding door had a secondary lock mounted on the inside near the top where the two sections meet. It is designed to prevent entry from the balcony for security purposes, but will be perfect for your desired use. I would assume the Oasis has a similar lock on its doors. I don't remember seeing one when I sailed on the Oasis, but you would not ordinarily notice it if you were not looking for it. I just happened to notice it on the Allure.
Freedom OTS B/B March 23 - April 6, 2014
Independence OTS April 26, 2014
Independence OTS -Transatlantic - May 4, 2014
Vision OTS June 9, 2014
Explorer OTS B/B November 29 - December 12, 2014
Quantum OTS - April 24, 2015