"Andy Dingley" wrote in message
...
On 19 Nov, 10:21, Peter Parry wrote:

Dennis, if you use 4 digits there are 10,000 possible combinations.

Nowhere near that number as you can only use each key once, so a
combination of 1234 is valid but 4433 cannot be used.

Nearly all of them are _either_ 4 independent digits (10000
combinations) or a selection of 0-10 digits where each digit is either
used once or not used and the order doesn't matter (1024
combinations).

The ones with wheels have many combinations but are easy to find the code
for each wheel if you know how.
The GE boxes are mechanical and all you have to do is press the correct
buttons in any order.

There are some electric locks with keypads that do have a large number of
combinations.

Although there are a few locks (a well-known brand used in offices)
that have a sequence of digits (i.e. fixed length, ordered) and also
forbid repetition, I've not seen that mechanism in a water-resistant
external form. They're also manipulatable.

A sequential drum combination (back & forth dial) is a nightmare on an
external door, as it needs good eyesight, good lighting, good motor
control and is generally unsuitable as an outside door lock, no matter
who's using it. If you need that level, go electronic. A combination
of keypad (carers) and simple cardlock might work, especially if it's
non-contact.