mechanical placebo
n. A device or object that appears to perform a specific function, but in fact does nothing at all.

Example Citations:
Consequently, most of the devices were deactivated by the later 1980s, but the buttons themselves and the signs bearing the instructions for their use remained in place. Evidently there was never any official announcement about the status of the "mechanical placebos."
—Henry Petroski, Success Through Failure, Princeton University Press, February 27, 2006

And surely the mechanical placebo of all times [sic] has to be the "Complaints"/"Suggestions" box?
—Marian Bantjes, "Information Design and the Placebo Effect" (comment), Design Observer, March 1, 2004

Earliest Citation:
The city deactivated most of the pedestrian buttons long ago with the emergence of computer-controlled traffic signals, even as an unwitting public continued to push on, according to city Department of Transportation officials. More than 2,500 of the 3,250 walk buttons that still exist function essentially as mechanical placebos, city figures show. Any benefit from them is only imagined.
—Michael Luo, "For Exercise in New York Futility, Push Button," The New York Times, February 27, 2004

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