What is the reason many elevators have concave shaped buttons. Like this:
Any special reason behind this?
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A really interesting question, we had a chat about it and decided it was probably one of four things:
1) Cost - if you're making a million lift buttons every year, maybe there's something about the manufacture that makes it cheaper to cut and grind several concave buttons than any other shape, assuming they're cut in bulk from single aluminium rods.
2) A concave button 'centres' the pressure from a button press every time. By controlling that pressure, the press will always centre itself on the underlying sensors and result in 100% successful hits.
3) Weight - all elevators have a weight limit. If you make concave buttons you're shaving a little bit of weight each time and maybe it all adds up. If the building has 40 floors that could be a kilo of weight saving per lift. (a stretch, we know, but possible)
4) Design language - it could just be that the designer thought they looked cool.
That's our two-penn'th.
I am not sure if it is a mandatory requirement but it seems that its easier to push a concave button rather than a convex one.
In the UK it is mandatory to have braille on-or next to the buttons and the lift needs to 'talk'- floor number, going up/down, door opening/clossing. and for partially blind people bright illumination- but that is not law yet.
So here is something that meets your question and should not go wrong. Braille and concave.
Some examples of 'other' elevators
With lift buttons it should be easy to press the intended buttons for everyone, while at the same time you should minimize accidental button presses. A concave button does a nice job at both requirements.
The shape of the button gives tactile feedback when you've found your target. This is especially relevant for people who experience difficulties in pressing the buttons. These are not only the blind, but also wheelchair users (who often use a stick for this purpose) and people with impaired balance. Because of the shape of the button your fingers don't slip off and you don't accidentally press the button next to it.
When you have to rely on touch to find the buttons it helps that they have a distinct shape. With flat buttons, just feeling for the button can result in an accidental button press. Non-handicapped people also lean against the wall or get pushed around (especially in crowded elevators) and may carry luggage.