I had the same happen at a St Regis where the maid entered my room while I was showering. What made it odd was since I only heard the door open but did not see anyone I asked the maid if she came in she denied it. So I asked security to check the cameras which they did and it turned out to be the maid...

Hotel staff did not seem to think it a big deal, which bothered me.

GM responded and all was good, turned put the maid was scared to say she was in there for whatever reason, the FD had not informed them of the late check out.

I lock my door at night but rarely at day time, maybe I need to revisit my theory ��