Jake Taylor was a stalker.

This. I always assumed that they left it open for their dinner party guests, to avoid hassles. Jake did seem surprised when the door opened and he was in the apartment.

No, it was clearly the lawyer's apartment.
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I was watching this last nite and my son brought up the point that perhaps it was not the apartment but like the building's clubhouse or something like that, a party room that was a common room that anyone could go in.
Glad to see that other people were bothered by this as it has bugged me for years.

There was a small party going on. I've seen places like that where the owner could unlock the elevator so no key was needed. Nobody ever used that feature but it was there.
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that golf cart was cool. eco-friendly too.
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Yeah usually in high-end living places(high rise condos/penthouses), a lot of these places do have elevators that open right up into the living quarters.
But like others have said: You either need a key or a security code to access the elevator, and another code to access your particular apartment/condo/penthouse.
So yeah, that scene was BS

He does this earlier in the movie too when he enters Lynn's boyfriend's apartment. I would be very worried living in a situation like that.

yea i see keys used for the half the places i go to here in downtown madison. its an urban apartment thing.
so yea OP, hed need a key for the front day and the elevator probably

well, i cant speak for houses/apartments that have elevators that take you to your apartment, but I have been in hotels where a certain floor was closed off to only the people with a room key to that floor. that scene always bothered me.

Have you ever used a key for an elevator?
I understand what you're sayingyou'd have to bypass security to get there. What seems unreasonable to me is that the elevator would open right into the apartment. Unless it were a private elevator, in which case it undoubtedly would be a little bit harder to access than it appears to be in the film.