[riffraff]

isn't this solved "well enough" with a code-lock holding a key? I've used it a few times and while it's low tech it seems pretty effective and costs about zero.

[Lucadg]

That's one of the best solutions when possible. Low tech, low cost, high usability.

Unfortunately in many cities, particularly in Europe, you are not allowed to stick a lock on the wall of the building.