In the UK, the majority I run into seem to be near-placebo, but they do actually work in particular scenarios, it's just influenced by an algorithm. The key on

In the UK, the majority I run into seem to be near-placebo, but they do actually work in particular scenarios, it's just influenced by an algorithm. The key one is Tube train buttons. For indoor stations, they are effectively placebo buttons, but once the weather gets very hot or cold and the Tube train is outdoors, they tend to become active. By the inconsistent way they're activated, I believe it's the train driver in control but that may be different on different lines. The part that interests me is just how many people fail to notice they have no effect indoors - whilst it's potentially difficult to spot with an isolated button (eg at a road crossing), it's blatant for the Tube as everyone's door opens at the same time and everyone emerges at basically the same time just after (with tiny variations). What stitches to tourists in London, is that it's the other way on UK railway trains (near London at least) - they usually do work always, and thus the inconsistency provides a further barrier to figuring it out!