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We've all seen it in the movies where a kid will push all the buttons in an elevator. We've all likely done it - accidentally hit the wrong floor.

There's no unselect after you select a floor in an elevator.

Why is that? It seems that it would be a useful feature but is there some sort of logical or UX reason why you would not implement an unselect feature?

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Another elevator design question that always bugs me - why don't they account for the ten minutes after five o-clock? I'm on floor 4 of 14, and by the time it gets to me it is full and it still stops at every floor. You would think it would be easy enough to put in a rule where if it has stopped at a certain number of times (without someone selecting a floor other than ground) that it will be full. –  Alex Apr 6 '12 at 6:11
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@Alex Another "I beg to differ" moment from me - I could be misinterpreting the cause but I've seen lifts that were apparently full or near the weight limit not bother stopping at a floor on the way down even though people outside had pressed the button to go down. The lift in question was a glass-doored shopping mall one so I could see them squashed in like sardines as they sailed on by. :) I heartily agree though - apart from the glass lift mentioned it happens to me a lot too. –  Xiaofu Apr 11 '12 at 7:49
    
Unselect would have cost more. –  Mathew Foscarini Sep 25 '12 at 18:21
    
I believe the usability is restricted by the underlying elevator scheduling algorithm. Older elevators have simple algorithms that don't allow for unselecting a floor. –  CJ Franken Nov 22 '12 at 8:37
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9 Answers

Then we would see kids in the movies unselecting all buttons. Since nobody is hurt if the elevator stops too often, it may be better to keep the interface as simple as possible. Hence, no unselect button.

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It's not just kids hitting every button... –  Alex Feinman Apr 4 '12 at 14:02
    
but if they unselect your floor, u'd just select it again. Doesn't seem that satisfying compared to making someone have to wait through every single floor to get to their destination. –  RoboShop Apr 4 '12 at 14:53
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I can see select wars. :) –  toscho Apr 4 '12 at 16:37
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I agree with toscho, but I'd like to add another argument: It can cause problems with the next person entering the elevator. People often just hit the button for the floor they want to go to, paying no heed if that button has been selected already (if such feedback is clearly visible at all). If you'd allow an unselect, neither of the people wanting to go to that floor will arrive there. That is, unless you add a whole new set of buttons for the unselect, but doubling the amount of buttons won't improve usability...

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Also, if a bulb is burned out (and elevator maintenance is often not as good as one would like), you can't tell its state. So long as pressing it can only turn it on, no harm done. Deselect doesn't necessarily require more hardware, as noted by @Xiaofu, but it does call for a different gesture. –  Monica Cellio Apr 4 '12 at 14:42
    
@MonicaCellio +1 for the bulb burn-out scenario –  Kartik G Apr 11 '12 at 5:15
    
@MonicaCellio - how about the push-button design? i believe it will address most state-related issues. –  Eliran Malka Feb 7 at 19:01
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I beg to differ - I've been in plenty of lifts where you can deselect a floor. It operates by holding onto the button for a few seconds until the light goes out (or sometimes by double-clicking the selected floor button to unselect it). It's possibly done in this way to preclude the problem @André was referring to - forcing people to make a deliberate choice to deselect rather than doing it accidentally.

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I'm going to try that –  benb Apr 4 '12 at 11:13
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Me too. From now on, in every elevator. –  Bart Gijssens Apr 4 '12 at 12:03
    
It sadly doesn't work in my apartment building (where naughty kids are most active), but I've certainly used it in office/skyscraper lifts here in China. It'd be interesting to know if only certain manufacturers have implemented this. –  Xiaofu Apr 4 '12 at 12:04
    
That brings ideas about adjusting priority. For example pressing with several sequence (i.e. short-short-long-short) you can set a number as urgent that would result elevator to skip pressed flats while reaching the urgent number. That might be used by executives. –  Cem Sağıroğlu Apr 4 '12 at 12:58
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Interesting, I never noticed. How would you discover such a feature, I wonder? –  André Apr 4 '12 at 15:41
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Having unselect option increases complexity and requires more scenarios to be accounted for, For instance, if the lone selected floor button gets unselected unintentionally, will the elevator halt mid-way? There is no critical use-case for unselect. Like @toscho pointed out "Since nobody is hurt if the elevator stops too often", there would be a slight delay but nothing critical.

So its best to follow the KISS principle!

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This is a good point. If I get a chance I'll try it. There could always be logic to prevent the last selected button being unselected. Or perhaps the lift would just go off to whatever holding floor it is set to if there's no requests from other floors pending. –  Xiaofu Apr 11 '12 at 8:10
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It's quite commonplace in Japan for lift buttons to have an 'undo' function - press to select, press to un-select - but I've never encountered it in the UK ever. Maybe it's because I'm not holding the button down for long enough over here, but I'm certainly going to try it from now on.

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Im some elevators there's a "Stop" button.

This button is usually marked with a red colour and placed nearby the alarm/emergency button.

If you press the button you can freeze the elevator and eventually make another choice.

It seems to be a discouraged action (location, warning colour) but it works..

enter image description here

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Seems like a troll, why would I press the alarm button if all I want to do is unselect my selection? I don't press the escape key when I want to unselect my text selection? –  MatthijsM Sep 25 '12 at 14:37
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It's not the alarm button. It's a separate button marked with "STOP" –  Rdpi Sep 25 '12 at 14:44
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Sorry, I misread your answer. But in the picture shown, I see a keyhole. I do not expect this keyhole to be asking for my carkeys ;-) Maybe we should have an 'elevator man' in every elevator again? –  MatthijsM Sep 25 '12 at 14:52
    
Yes, seems to be a Keyhole.. discourages even more –  Rdpi Sep 25 '12 at 14:57
    
In Italy, there is a button to stop the elevator, and it is normally used to stop the elevator when you selected the wrong floor, and you notice it before the elevator's doors are completely closed. The con is that the same button stops the elevator when it is moving. (I am too scared about elevators that I would not touch it while it is moving. :)) –  kiamlaluno Oct 1 '12 at 7:04
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I have seen elevators with an unselect option where pressing the floor button after selected deselects it. However I believe the primary reason behind preventing people from cancelling a selection was to account for the case of an user entering the elevator and proceeding to cancel all other selected floors in an hurry to get to his destination (or just because he felt like being a jerk).

The lack of a cancel button would also force people to pay attention to their choice as there was no apparent revert option hopefully preventing a reduction in a number of random selects

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We have an elevator at work with two sets of numbers on both sides of the door. Also when you click a selected floor it deselects it. Many times it happens that I press my floor number and someone else comes in immediately after me and presses the same floor number on the other set of numbers, thus deselecting it.

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I think, historically, the usability was restricted by the scheduling algorithm. If you cancel a floor selection, the scheduling algorithm has to re-calculate its schedule. Depending on the simplicity of the algorithm, this may not be possible/worthwhile. For an overview of factors that are taken into account in elevator scheduling algorithms, have a look at this Quora answer.

I believe the reason why modern elevators are supporting cancelling floors is simply because they have better scheduling algorithms that allow for this added complexity.

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