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Comment by jamesbkel | Hacker News Reader

Did you consider the idea of a combination (circular) lock?

I suppose it may be possible to decipher the stopping points, but if there's a final circle to confirm the code/cover them up, I could see that working.

edit: added "(circular)" to clarify

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A rotary dial lock seems like it would be a good idea... Especially if the set number of digits was variable. All you'd see is a round smudge.

You could fix this by randomizing the orientation of the lock.

I think that's exactly what I thought when I read his comment. I'm not sure why anyone else thinks it's a bad idea, though.

Let me clarify it a bit: Just like a rotary telephone, the numbers are in a circle. To open the lock, you drag your finger in a circle around the ring, alternating left and right like a combination lock.

But to make sure the smudges are meaningless, the device rotates the rings randomly before each attempt.

You still enter the same code, in the same pattern, but the rotation of the device changes each time.

That would be a usability nightmare if I am picturing what you are saying correctly.

It wouldn't be that bad to have it start on a different number every time. It means that you would have to actually pay attention to the unlock process though, muscle memory wouldn't work.

I think if this worked like setting 'an alarm time' on iOS, it would work. I can't see how one would know where a dial's 'rotation' stopped; specially if the 'dials' always started from a random digit.

Let's say your combo is 74798; one occasion the unlock shows 31920, next 88935, etc. but never opening the phone on a collision. So if it lands on 74798 (your current combo), it would not unlock the phone automatically.

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