Hitting the button a second time would undo the call. You should also be able to undo the calling the elevator button from outside. Say you on the ground floor and the elevator stops on the way down to the basement. You could get on and then skip the stop on the way back up -- if there was a way to cancel the request.

Barry,

I don't find I can cancel the request by "Hitting the button a second time". Where do you use the evlevator?

Possible disadvantages of this idea:

Anally retentive "high achieving" types would cancel your floor so they could get to their own floor faster, especially if the elevator is crowded and no-one else can get at the control panel.

Muggers could cancel your floor to trap you, or force you to get out on a floor of their choosing.

If the light bulb in the button fails, you won't know if you've selected your floor or not. You will probably press the button a few times waiting for the light to come on, and then will be stuck trying to remember if you pushed it an odd or even number of times.

Elevators stacked in multiple banks (e.g. in large high rise buildings) use a complicated algorithm to schedule the optimal arrival times of different elevators at different floors. Cancelling a floor after setting off but before arriving there would screw up the algorithm and cause an elevator "traffic jam", so the most efficient thing would be to still go to that floor anyway, obviating the advantage of cancelling.

At present, a stuck button usually results in the car always the visiting the affected floor, which is mildly annoying. With press on/off a stuck button could result in either _never_ visiting that floor, or doing so randomly. Either condition is much worse than the mild annoyance of always visiting it.