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Do elevators need call buttons? Shouldn't the elevator be called if someone stands in front of the door? I see many questions about people pressing the buttons for different banks of elevators and so on, but you can only stand in one place. And, if the person walks away, the call is cancelled.

Based on having reliable people sensors already, why not just dispense with the buttons, or make them unnecessary? They could still light up when a person was sensed. If the person actually wanted the other direction, they could press it, but normally no press would be required.

What is the failure of this idea?

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I’ve seen elevators that default to having one car return to the ground floor, and the door stays open. No sensor needed. It’s nice.

The other floors, though? What if I’m on Floor Five and saying goodnight to a colleague on a business trip (in a neutral space) and the elevator detects our presence and just… waits for us to get in? But we don’t want to? Is it worth making us feel awkward while the elevator could be somewhere else?

Another thing buttons with indicators (like lights) do is give us a feeling of being in control of the system, and letting us know that the system is responding. Buttons give us a precise moment to request a task, which can be a good experience when we’re in a hurry and need to feel in control. Sensors have a more passive feeling.

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I have seen many variations in the design of elevators, and I can think of some complexities in not having call buttons. Ultimately it comes down to the difficulty in optimizing the efficiency of the elevators with limited information.

I can think of a similar problem that happens with pedestrian crossings and the scheduling of traffic lights. In some countries there are sensors installed either in the road or on the above ground fixtures to provide traffic data that can be used to adjust the timing of traffic lights. However, during times of peak traffic, often it is more efficient to stick to a simple timing schedule instead of something too complex to manage well. This is why some pedestrian crossings don't have push buttons because the pedestrian light is scheduled in automatically, while others have the push bottons (not to speed up) to allow the pedestrian light to be scheduled in.

I have seen buildings where a concierge simply asks people which floor they want to go to, and the floor is pressed before they approach the waiting area for the elevator. It is similar to not having to press a call button, but still allows some input data to help optimise the elevators.

I can imagine a situation where a building is very full or busy on a Monday, and using sensors to help manage the elevators might not be much better than simply having call buttons. Of course, if you were on the top or bottom floor then there is only one direction possible, and if you had some data linked to the levels that a person can access you could make an educated guess, but I don't see this as being much more efficient then having the call buttons because it is still better to design a system where you can reliably get the outcome that you are expecting most of the time.

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The idea fails with direction of travel.

You can assume that a person waiting wants to go down: the sensor detects his presence and lights an indicator showing "Down".

What if he wants to go up? A lift already going up could call at the floor and collect him on the way. How does he cancel the automatic "Down" request? If this is a button press to signal "Up", there's no saving: he still needs to press a button to cancel the "Down" assumption.

What if there are two people who want to go in opposite directions? A lift could stop on its way down or on its way up, but there's no way to indicate that requirement. If pressing a button actually cancels the assumption (as in the previous counter-example), then you've created another problem because only one request can be in play at once.

Far better to have people signal what they actually want the system to do: "Take me down"; "Take me up"; "Stop in either direction because both are needed."

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There are three main types of elevators:

  1. Classic/Analog: These are the ones that have been in use since their invention, regardless of the different mechanisms they may employ.
  2. Automatic: These elevators have a memory for pressed buttons, both for callers and riders.
  3. Smart: These elevators utilize complex algorithms to determine various variables, including which floor to stop on. These algorithms can be configured by administrators. For instance, all idle elevators on the ground floor or evenly distributed across all floors.

(there are other types, but they're specialty elevators and the caller mechanism falls into one of these three categories)

However, all of them require being called. This is based on the Principle of Intentionality, where users convey their intentions when interacting with the system. For example, suppose I call the elevator and then realize I forgot something. So I quickly return to my office to retrieve it and then head back to the elevator. I would expect the call to remain active. I never interacted with the system in a way that would change my original intention.

Furthermore, a caller button follows an accepted pattern with a clear affordance for most users. Not finding a button would be highly confusing for the majority of users.

Last but not least, it's important to note that physical buttons are more durable than using motion detectors. Additionally, repairing buttons is both faster and more cost-effective than fixing a motion detector. This means that relying on a motion detector may lead to numerous issues that wouldn't exist otherwise, with minimal if any advantages.

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