If you're worried about people stealing your stuff, lockable hard luggage is more difficult to get into or walk away with, but of course not foolproof. I have a couple of soft bags that literally zip right off. If someone wanted my things they could just walk up, zip off the bags and walk away. But I only use them for carrying stuff that I don't want on my person while I'm on the bike, or drinks and snacks. If I put my wallet or jacket in the bag it comes out when I stop. I haven't had the need yet for anything more than that.
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There are no automatic doors, just very polite ninjas