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A placebo button (also referred to as an idiot button) is a push-button with apparent functionality that actually has no effect when pressed. They are commonly placed in situations where it would have once been useful to have such a button but the system now proceeds automatically.
Although non-functional, the buttons can give the user an illusion of control. In some cases the button may have been functional, but may have failed or been disabled during installation or maintenance or was, in a relatively small number of cases, installed to keep people contented, much in the same way as placebos.
In many cases a button may appear to do nothing but in fact cause behavior that is not immediately apparent; this can give the appearance of it being a placebo button.
Despite media reports to the contrary, "door close" buttons in elevators are not placebo buttons in the common sense. This myth has been popularized in part because, during automatic (normal) operation of passenger elevators, the "door close" button often has no observable effect. However, the button is not added simply as a placebo. A functional "door close" button is required by elevator code (ASME A17.1, Requirements 188.8.131.52, "Phase II Emergency In-Car Operation"). For firefighters and rescue personnel to open or close elevator doors during emergency operation, the "door open" and "door close" buttons must be pressed continuously until the door is opened or closed respectively. An elevator with a non-working "door close" button would receive a violation during a routine inspection and test of fire service. Much like the "door close" button, the "call cancel" button is normally not functional during automatic operation, but allows firefighters to change the destination of the elevator mid-flight during emergency service.
London Underground 1992 stock, 1995 stock and 1996 stock include door control buttons. The doors are normally driver operated, but a switch in the driving cab can hand control to passengers once the driver activates the buttons, much like mainline railway stock. In addition, London Underground D stock used on the District line were built with door open buttons which worked much like those of the 1992, 1995 and 1996 stock. These buttons were subsequently removed when the stock was refurbished. Trains on the Central Line, DLR and Overground all have buttons, with current Central Line stock retaining both open and closed buttons that are no longer active. S-series stock, still being deployed on the Underground network, also has door buttons. Although inactive in general use, these are capable of sometimes being placed in manual-open mode at stations, giving them an actual non-placebo function at those times.
Office thermostats 
It has been reported that the temperature set point adjustment on thermostats in many office buildings in the United States is non-functional, installed to give tenants' employees a similar illusion of control. In some cases they act as input devices to a central control computer but in others they serve no purpose other than to keep employees contented.
A common implementation in buildings with an HVAC central control computer is to allow the thermostats to provide a graded level of control. Temperatures in such a system are governed by the central controller's settings, which are typically set by the building maintenance staff or HVAC engineers. The individual thermostats in various offices provide the controller with a temperature reading of the zone (provided the thermocouples are not installed as inline duct sensors), but also serve as modifiers for the central controller's set point. While the thermostat may include settings from, for example, 60 to 90 °F (16 to 32 °C), the actual effect of the thermostat is to apply "pressure" to the central controller's set point. Thus, if the controller's setting is 72 °F (22 °C), setting the thermostat to its maximum warm or cool settings will deflect the output temperature, generally by only a few degrees Fahrenheit (about two degrees Celsius) at most. So, although the thermostat can be set to its lowest marking of 60 °F (16 °C), in reality, it may only change the HVAC system's output temperature to 70 °F (21 °C). In this case, the thermostat has a "swing" of 4 °F (2 °C) — it can alter the produced temperature from the main controller's set point by a maximum of 2 °F (1 °C) in either direction. Consequently, while not purely a placebo, the thermostat in this setup does not provide the level of control that is expected, but the combination of the lower setting number and the feeling of a slight change in temperature can induce the office occupants to believe that the temperature was significantly decreased.
See also 
- Lockton, Dan (2008-10-01). "Placebo buttons, false affordances and habit-forming". Design with intent. Retrieved 2009-07-28.
- Luo, Michael (2004-02-27). "For Exercise in New York Futility, Push Button". New York Times. Retrieved 2009-07-28.
- Paumgarten, Nick (2008-04-21). "Up and Then Down — The lives of elevators". The New Yorker. Retrieved 2009-09-02.
- "George" from Barnet, UK, "Why do tube trains have unused door buttons?", London's Biggest Conversation, retrieved 2012-08-26
- District Dave, "D78 Stock In Works", District Dave's London Underground Site, retrieved 2012-08-26
- "Why Are There Buttons On Tube Train Doors?". Londonist. April 11, 2013.
- Sandberg, Jared (2003-01-15). "Employees Only Think They Control Thermostat". The Wall Street Journal. Retrieved 2009-09-02.
- Katrina C. Arabe (2003-04-11). ""Dummy" Thermostats Cool Down Tempers, Not Temperatures". Retrieved 2010-02-13.