What's the down side of a dynamic numbered radial keypad?
There is a Security User Experience (SUX) downside, which you might consider to be minor.
As someone who is more kinestheticly inclined, I don't memorize things like phone numbers or PINs: I memorize patterns. If I was forced to use this keypad, I would have to use a compensating method to remember the actual digits (like writing it down).
While not everyone is strongly kinesthetic, it is a factor in how people learn, which means that others might need to write down the passcode, too. This, of course, defeats the purpose of having a dynamic keypad.
As I say, it might be a minor point, but it is a downside that impacts security.
I can think of several possible downsides to this sort of circular dynamic display:
- The dynamic display slows down the user entering the access code. Because the numbers will not be located in the same place every time the user needs to stop and read the keys before pushing the appropriate button. This may take only a second or two longer than a traditional keypad but additional time could allow a second pair of eyes to better observe the number layout as well as the keys punched.
- The dynamic display requires the user read the keypad. With static number pads, everyone knows the layout so it is easier for a person to enter their code without looking at the key numbers. This means that a person can more closely stand to the keypad as to block the view of any "peeping Toms". With a dynamic keypad the user must more closely read the keys which means that they will naturally stand farther away from the console, allowing more space for wandering eyes to observe.
- The circular design spaces the keys farther apart than a square layout. You mentioned that you can intuitively tell which buttons are being pushed based on the known static keypad layout but assume you didn't know where 0-9 was located on a square keypad. One of the nice things about a square keypad is that the numbers are bunched together so an individual can somewhat block the view of the keypad with a hand while pushing buttons. With a circular design, your hand would be more splayed out making it much more obvious which buttons are being pushed than a square pad. This weakness is clearly mitigated by the dynamic numbering but I can't help wonder if a square dynamic pad would have been better for concealing the buttons being pushed.
- It can be argued whether this is necessarily a weakness but I do notice that this keypad clearly has an electrical dependency. Mechanical locks have their own strengths and weaknesses but it is important to note that electrical locks can be vulnerable to power outages and surges as well certain types of electrical tampering. In that same vein... these types of electrical doors are typically hooked up to a network which allows for computerized vulnerabilities as well.
As mentioned in other posts, there are a whole lot of advantages to this design as well, though, so I suppose with this keypad you are trading fingerprint smudge vulnerabilities for "looking over the shoulder" vulnerabilities which could easily by limited with proper training.
There pretty much isn't a downside, aside from cost and design complexity. From what you've shown it looks like the numbers randomly cycle across the buttons, so there's no set pattern to watch. These types of keypads are quite common in prisons, where the pads are quite close to cells or are in communal areas (e.g. the dining hall or laundry areas) and sneaky prisoners will watch the guards day after day to guess the pin pattern.
I'm not sure if the circular design helps, but I guess it's slightly harder to identify which button was pressed. I can't say I've got anything to base this on, though.
As for why they aren't commonly used in safes? Cost and simplicity is probably the biggest factor, but also the fact that safes usually aren't repeatedly opened in front of potential threat actors (e.g. in a public space) but are rather in a closed off area such as your house, or in a back room of a bank.