Simplex 5-button combination locks
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
(*Hobbit*'s in-depth evaluation)

     This deals with the Simplex or Unican 5-button all-mechanical combination
locks.  They are usually used in a variety of secure but high-traffic
applications, and come in a number of flavors: dead bolt, slam latch, lock
switches for alarms, buttons in a circle or a vertical line, etc.  The internal
locking works are the same across all of these.  Herein will be described the
mechanical workings and a method of defeating the lock that falls out by
logical inference and observations from playing with it.

The internals

     Caveat: If this seems unclear at first, it is because the absolutely best
way to understand the inner mysteries is to take a Simplex lock apart and study
it.  It is highly recommended that the reader obtain and disassemble one of the
units while studying this; otherwise the following may be confusing.  The
locking mechanism box is swaged together at each end, but it is trivial to open
up without destroying it.  To set a lock up for study, remove the back, leaving
the front plate held on by its Jesus clip.  Put a spare thumb turn down over
the shaft so you have something to grab.  Take care not to lose the button
connecting pins; they drop out.

     In the round configuration, the buttons talk via bent bars in the
faceplate to the same vertical column as the straight ones.  Thus all buttons
henceforth shall be referred to as if they were in a straight vertical row,
numbered 1 to 5 reading downward.  The actual locking mechanism inside is a
small metal box, about 3 inches high and .75 x .75 inch across the base.  It
contains five tumblers, one corresponding to each button, a common shift bar,
and a couple of cams to handle reset and unlocking.  The user dials the
combination and turns the handle to the right to open the lock, or to the left
to reset any dialed digits if he made a typo.  If the proper combination has
not been diald yet, the shaft will not turn to the right.  Setting a
combnation shall be described later.  Some of the linear-style locks are
actually made by Unican, but have the Simplex box inside.  For these, a
clockwise twist serves as both open and reset.  There is a detent plate and a
screwy lever system; if the lock is not open yet, the lever cannot turn to the
*box*'s right.  The detent slips, allows the levers to shift the other way, and
the box arm is then turned to the left.  If the detent does not slip, it's
open, and the plate locks to the latch shaft and pulls it back.

     Each of the five tumblers has six possible positions.  Each button does
nothing but push its corresponding tumbler from the 0 position to the 1
position.  Therefore, each button can only be used once, since once the tumbler
has moved, the button has no further effect.  The trick comes when *subsequent*
buttons are pushed.  Each button press not only shoves its tumbler from 0 to 1,
it also advances any "enabled" tumblers one more step.  When a tumbler is
enabled, its corresponding gear has engaged the common bar and pushed it around
one position, so the next button press will do this again, thus taking
previously enabled tumblers around one more notch.  This way, the further-in
tumbler positions can be reached.  It can be seen that there are undialable
combinations; for instance, only *one* tumbler can reach position 5 for a valid
combination [Positions labeled 0 thru 5, totalling six].  If one sits down and
figures out possible places for the tumblers to go, many combinations are
eliminated right away, so the number of possibilities is *not* 6^5 as one might
expect.  Two-at-once pushes are also valid, and are *not* the same as pushing
the given two in some other order.  Pushing two [or three or ...] at once
simply enables two tumblers at once and shoves them to position 1 at the same
time.  [This of course leaves less buttons unused to push them in farther!] The
tumblers themselves are small round chunks of metal, with gear teeth around the
top half and a notch cut into the bottom edge.  When all these notches line up
with the locking bar, the lock is open.  The tumblers are mounted on a vertical
shaft so they can spin, with the locking bar fingers resting against the bottom
of each one.  The locking bar is prevented from rising if any notch is turned
away from it.  Juxtaposed to the tumblers is another shaft containing idler
gears, which in turn talk to the common bar in the back.  The intermediate
shaft slides up and down and makes combination changes possible.  Note: The
buttons actually talk to the idler gears and not the tumblers themselves.  This
is necessary since during a combo change, the tumblers cannot move because the
locking bar teeth are sitting in the notches.

[Editor's note:  Simplex locks are set at the factory with a default code of
(2-4), 3.  This is often not even changed.]

Combination change, other random facts

     Once you know the current combination, you might want to change it.
Instructions for doing this undoubtedly come with the lock; but it's real easy.
There is a screw in the top with a hex hole; remove this from the lock body.
Dial the proper combination, but don't move the handle.  Press straight down
through the hole with a small screwdriver, until you feel something go "thunk"
downward.  The lock is now in change mode.  Reset the tumblers [leftward
twist], enter your new combination, twist the handle as though opening the
lock, and your change is now in effect.  Re-insert the screw.  This does the
following: The thing you hit with the screwdriver pushes the tumblers down onto
the locking bar [which is why the proper combination must be entered], and
disengages them from their idler gears.  Button presses turn the *idler*
*gears* around, and then the opening action shoves the tumblers back up to mesh
with these gears in their new positions.  A subsequent reset mixes the tumblers
up again to follow the new combination.  This description is admittedly
somewhat inadequate; the right thing to do is take one of the locks apart and
see for one's self what exactly happens inside.

     The Unican model has a disk-locked screw on the rear side.  Removing this
reveals a round piece with a flat side.  Twist this clockwise to enable change
mode as in the above.  This lock, of course, would be a little more secure
against random people changing the combination for fun since you ostensibly
need a key to get at it.  Keep in mind that "reset" on these is done by turning
the knob all the way *clockwise* instead.  There is a linkage that ensures that
the shaft inside goes counterclockwise for the time that change mode is
enabled.

     It is amusing to hear local locksmiths call the Simplex internals a
"computer".  It would seem that none of them have taken one apart to see what
is really inside; the box is painted black as far as they are concerned and
non-openable.  Obtaining one is the unquestionably best way to learn what's in
there.  Unfortunately they cost on the order of $120, a price which clearly
takes advantage of the public's ignorance.  These locks are *not* pick-proof
after all, and anyone who maintains that they are is defrauding the customer.
There are a variety of ways to increase the picking difficulty, to be discussed
elsewhere.  Your best bet is to borrow one from somewhere for an evening and
spend the time learning its innards.

Determining an unknown combination

     Contrary to what the marketing reps would have you believe, the locks can
be opened fairly quickly without knowing the set combination and without
damaging the lock.  Through a blend of a soft touch, a little hard logic, and
an implicit understanding of how the locking mechanism works, they generally
yield within five minutes or so.  [There are *always* exceptions...]

     This method requires that one does not think in terms of a sequence of
button presses.  One must think in terms of tumbler positions, and simply use
the buttons to place tumblers where desired.  For practical description
purposes, it will be assumed that the buttons connect right to the tumblers,
rather than the idler gears that they really do.  The idler gears are a
necessary part only during combination changes.  Unless you are doing a change,
considering it this way is pretty close to the facts.  Remember that a 0
position means the button was never pushed, and 5 is enabled and shifted as far
as possible.

     Turning the thumb handle to the right [clockwise] raises the locking bar
against the tumblers.  Since the lock is never machined perfectly, one or more
tumblers will have more pressure on it than other ones, and this shows up as
friction against it when it is turned via the button.  This friction is felt in
the short distance between fully-extended and the detent on the button [the
first 2 or 3 mm of travel].  Some will travel easily to the detent, and others
will resist efforts to push them in.  Suppose you are twisting the handle, and
tumbler 1 has lots of pressure on it [you can feel this when you try to push
button 1 in].  When you back off the tension on the handle a little bit, the
button can be pushed in against the resistance.  The fact that the button has
resistance at position 0 tells you that tumbler 1's proper position is *not* 0,
or there would be no pressure if the notch was there!  Upon pushing button 1
in, you find that no pressure has appeared at any other button.  This
eliminates position 1 for tumbler 1, also.  Now, how do you get tumbler 1 to
different positions so you can test for pressure against other ones?  Push
subsequent buttons.  Push any other button, and tumbler 1 advances to position
2.  Ignore what the other tumblers are doing for the moment.  Now, perhaps
another button has some resistance now.  This means that tumbler 1 is either at
the right position, or getting close.  Basically you are using other tumblers
to find out things about the one in question.  [Keep in mind that the first one
with friction won't *always* be tumbler 1!  Any tumbler[s] could have the first
pressure on them.] Continuing, push another "don't care" button.  A "don't
care" button is one that is not the one you're trying to evaluate, and not the
one that recently showed some friction.  What you want to do is advance tumbler
1 again without disturbing anything else.  Did the pressure against your test
tumbler get stronger, or disappear?  If it got stronger, that points to an even
higher probability that tumbler 1 is supposed to be at 3, rather than 2.  If
the pressure vanished or became less, 1 has gone too far, and you were safer
with it at position 2.  Let's assume that the pressure against your test
tumbler increased slightly when tumbler 1 was at 2, increased even more when
tumbler 1 was at 3 and vanished when you pushed it onward to 4.  Reset the
lock.  You now know the proper position of tumbler 1 [that is, whatever tumbler
first had pressure on it].  You've already drastically reduced the number of
possible combinations, but you aren't finished yet.

     You can now eliminate positions for the next one or two tumblers the same
way -- but to set things up so you can feel the pressure against these, you
must ensure that your newly-known tumbler [1 in this case] is in its proper
position.  It is useful to make a little chart of the tumbler positions, and
indicate the probabilities of correct positions.

                Positions

             0  1  2  3  4  5
             ----------------
        1 :  L  L  +  T  L  |   <-- Indicates that tumbler 1 is not
                                0, not 1, maybe 2, more likely 3.
Tumbler 2 :  |  |  |  |  |  |
number
        3 :  |  |  |  |  |  |

        4 :  L  |  |  |  |  |   <-- Indicates that tumbler 4 is not 0.

        5 :  |  |  |  |  |  |

     This chart is simply a bunch of little vertical lines that you have drawn
in a 5x6 matrix; the topmost row corresponds to button 1 and the lowest to 5.
Mark the probabilities as little hash marks at the appropriate height.  The
leftmost bar indicates position 0, rightmost 5; a high mark on the left side
indicates that the tumbler is 0, or is never used.  The relative heights of
your tick marks indicate the likelihood of the notch on the respective tumbler
being there.  If you don't know about a position, don't mark it yet.  This
chart serves as a useful mnemonic while learning this trick; as you gain
experience you probably won't need it anymore if you can remember tumbler
positions.

     A tumbler at the 0 position is already lined up before any buttons are
pressed.  This will feel like a lot of loose play with a little bit of pressure
at the end of the travel, just before the enable detent.  Be aware of this;
often enough the first button with pressure can be a 0, and if you aren't
watching for 0 positions you can easily assume it's a don't care, push it, and
screw your chances of feeling others.  Make sure your "don't care" test buttons
aren't supposed to be at 0 either.  It's a good idea to run through and try to
find all the zeros first thing.

     Let us continue from the above.  You have found that tumbler 1 is most
likely to bet at position 3, with a slim chance of position 2.  This is marked
in the above chart.  The reason this can happen is that the tops of the locking
bar teeth are slightly rounded.  When the tumbler is one away from its opening
position, the locking bar can actually rise higher, since the notch is halfway
over it already.  So don't assume that the first increase in pressure on other
buttons is the right position for the one you're finding out about.  Let's
assume that the next pressure showed up on button 4.  You can feel this when
tumbler 1 is at position 3; to get tumbler 1 out there, let's say you used the
sequence 1,2,3.  2 and 3 were your "don't care" buttons used only to push 1
around.  Therefore now, tumbler 1 is at position 3, 2 is at 2, and 3 is at 1.
5 and 4 are at 0, and can therefore be felt for pressure.

     The next step is to find the proper position for the next button with
pressure against its tumbler.  Many times you'll get more than one that exhibit
pressure at the same time.  Figure out which button has more pressure on it now
with your first tumbler in the right position.  In this example, only 4
applies.  You now want to advance tumbler 4 to different places, *while*
keeping 1 at its proper place.  1 must always advance to 3 to free the locking
bar enough to press on other tumblers.  To place tumbler 1 at position 3 and 4
at position 1, you would do something like 1,2,4 and check 3 and 5.  To place
tumbler 1 at position 3 and 4 at 2, you would do something like 1,4,2.  To
place 1 at 3 and 4 at 3, you have to press 1 and 4 at the same time, and then
advance that mess by two positions.  If you use 2 and 3 for this, the notation
is (14),2,3, which means 1-with-4, then 2, then 3.  You can also do 4,1,2,5 to
put 4 at 4 and check 3.  If all these tests fail, that is, no pressure appears
at any other button, you can start assuming that 4 is supposed to be way out
there at position 5.  For the example, let's say you did 1,4,2 and pressure
showed up on button 3.  To double-check this, you did (14),2,5, and the
pressure on 3 went away.  So tumbler 4 must have gone too far that time.  Place
a fairly high tick mark on the chart at tumbler 4, position 2 to indicate the
probability.

     Note: A better way to do that last test, to avoid ambiguity, is to do
1,(42),5 and check 3, then do (14),2,5 and check 3.  This ensures that the only
change you have made is to move tumbler 4 from 2 to 3 an avoids the possibility
of movement of tumbler 2 giving bogus results.  Through the entire process, you
want to try to change one thing at a time at every point.  Sometimes one of
this sort of possible test setup won't tell you anything and you have to try
another one [in this case, perhaps 1,(45),2 and then (14),5,2 while checking 3.
This has simply swapped the positions of 2 and 5 during your testing].

     You now know two tumbler positions, with a high degree of confidence, and
have further reduced the possible combinations.  From here, you could mix
tumblers 2,3 and 5 into the sequence with various permutations, as long as you
place 1 and 4 correctly every time.  This would still take some time and brain
work ...  let's try to find out something about some other buttons.  Place 1
and 4 where they're supposed to go ...  the sequence 1,4,2 will do it, and see
what's up with the other buttons.  1,4,3 will leave 2 and 5 available.  You
find eventually that 2 and 3 have the next bit of pressure distributed between
them [and are nonzero], and 5 feels like a 0, as described above.  To confirm
this, advance 5 along with some other button and check 3.  Bingo: There is no
pressure on 2 when 5 is enabled [and you have not changed anything else besides
5's position], so you can firmly decide that 5 is 0 after all.  So leave it
there.  [You did this by advancing 1 to 3 and 4 to 2, as usual, so you can feel
2's pressure in the first place.]

     By now you should know the proper positions of three of the tumblers, and
have eliminated any other zeros by feeling their initial pressure.  Now, since
2 and 3 have the next pressure on them, try and find out more about them.  You
know they aren't zero; suppose we try 1?  To do this you must get one of them
to 1, 1 to 3 as usual, 4 to 2, and leave 5 alone.  How?  Use hitherto unknown
buttons as dummies to position the tumblers right.  For instance, the sequence
1,4,3 will do what you want here; you then check pressure on 2.  Or 1,4,2 and
check 3.  Here you may notice that the pressure on the leftover is a *little*
stronger than before, but not enough to make any sure judgement.  Well, now you
want to advance an unknown to position 2 - but you suddenly notice that if you
do [by doing something like 1,(42),3] there are no free buttons left to test
for pressure!  'Tis time to try possibilities.  Your only unknowns are 2 and 3
now.  You must now advance 1 and 4 to their proper positions, leaving 5 alone,
while sprinkling the unknowns around in the sequence in different permutations.
Use your chart to remember where the known tumblers must go.  Sometimes you get
two possibilities for a tumbler; you must work this into the permutations also.
In this particular example, you know that either 2 or 3 [or both!] must be the
last button[s] pressed, since *something* has to get pressed after 4 to advance
4 to position 2.  An obvious thing to try is putting both the unknowns at
position 1 by doing 1,4,(23).  Try the handle to see if it's open.  No?  Okay,
now leave one of the unknowns down at 1 and mix the other one around.  For
instance, for 2 at 1 and 3 at 2, you do 1,(34),2 -- nope.  Advance 3 one more;
(13),4,2 *click* -- huh??  Oh, hey, it's *open*!!

Well, when you are quite through dancing around the room, you should know that
your further possibilities here ran as follows:

        3,1,4,2    ; to end the permutations with 2 at 1
        1,(24),3   ; and permutations involving 3 at 1.
        (12),4,3
        2,1,4,3

     One may see how things like 2,1,(34),x are eliminated by the fact that 1
must get to 3, and 5 must stay still.  Since only 4 buttons could be used, no
tumbler can get to position 5 in this particular combination.  Note also that
the farther *in* a tumbler has to go, the earlier its button was pressed.

     If all this seems confusing at first, go over it carefully and try to
visualize what is happening inside the box and how you can feel that through
the buttons.  It is not very likely that you can set up your lock exactly as
the example, since they are all slightly different.  Substitute your first-
pressure button for the 1 in this example.  You may even have one that exhibits
pressure against two or more tumblers initially.  Just apply the
differential-pressure idea the same way to find their most likely positions.
The example is just that, to demonstrate how the method works.  To really
understand it, you'll have to set your lock up with some kind of combination,
and apply the method to opening it while watching the works.  Do this a few
times until you understand what's going on in there, and then you'll be able to
do it with the lock assembled, and then in your sleep, and then by just waving
your hands and mumbling....

     A 5-press combination makes life a little tougher, in that you lose
versatility in your freedom of test positions, especially if your first-
pressure tumbler is at position 5.  Here you can use the "almost" feature to
your advantage, and advance the errant tumbler to one before its proper spot,
and hope to see increased pressure on other tumblers.  When a tumbler is one
away from right, the locking bar tab is hanging a large section of itself into
the tumbler notch, and the tab's top is slightly rounded.  So it can rise a
little higher than before.  If you twist the handle fairly hard, you can
distort the locking bar slightly and make it rise higher [but don't twist it
hard enough to break away the safety clutch in the shaft!] The chances of
someone setting this sort of combination without prior knowledge about the
*specific* lock are almost nonexistent.

     As if that wasn't enough, the next thing to deal with is the so-called
"high-security" combinations involving half-pushes of buttons.  The long
initial travel of the tumbler permits this.  If you look at your open mechanism
and slowly push in a button, you'll see that the tumbler actually travels *two*
positions before landing in the detent, and further motion is over one position
per press.  There is no inherently higher security in this kind of combination;
it's just a trick used against the average person who wouldn't think of holding
a button down while twisting the latch release.  It's quite possible to defeat
these also.  When you are testing for pressure against a tumbler set at
"one-half", you'll feel a kind of "drop-off" in which there is pressure
initially, and then it disappears just before the detent.  Before testing
further buttons, you'll have to "half-enable" the appropriate "one-half"
tumblers so the locking bar can rise past them.  Set your lock up with a couple
of combinations of this type and see how it works.  Note that you must hold
down the "half" buttons just before the detent click while setting or opening.
This makes an effective 7 positions for each tumbler, but in a standard [no
"halfs"] setup, it's effectively 6.  This is Simplex's "high-security" trick
that they normally only tell their high-dollar military customers about.  After
working the lock over for a while, it's intuitively obvious.

     The Unican type has no direct pressure direction of twist; if you turn too
far to the right you only reset the tumblers.  What you must do is hold the
knob against the detent release just tight enough to press the locking bar
against the tumblers inside the box but not hard enough to slip the detent.
There is a fairly large torque margin to work with, so this is not difficult to
do.  Unicans do not twist to the left at all, so ignore that direction and work
clockwise only.

Possible fixes

     The obvious things improvements to make are to cut notches of some kind
into the locking bar teeth and the tumblers, so that the pressure can't be as
easily felt.  Another way might be to have a slip joint on the locking bar that
would release before a certain amount of pressure was developed against it, and
thus never let the tumblers have enough pressure against them to feel.  The
future may see an improved design from Simplex, but the likelihood does not
seem high.  They did not seem interested in addressing the "problem".

