Many people use the key lock boxes manufactured by the Supra lock box company. This is a metal box, usually fixed to the wall by the front door, with 10 buttons on the front which you press to enter the secret combination.

Isn’t this an odd article for Bug Advisor?

This article began when we arived at our rental villa in Florida and realised that we’d forgotten the lock box code. I sat in the rental car, running the air con, wondering how many possible combinations would it take for me to open the box. After a long flight, my girlfriend just wanted me to call the management company and ask for the code – writing down a sequence of possible numbers didn’t make me very popular. So no bugs but travel was involved.


Oregon real estate agent, Delbert Williams, was annoyed by the amount of time it took to chase down keys of listed properties in the busy post-war real estate market of the early 1950s. His frustration compelled him to invent a secure key holder which combined a sand-casted metal container and a Yale bicycle lock.

The success of this product (which became the predecessor of the current day portable key box and eventually led to the development of the pushbutton lock) resulted in his forming Supra Products in 1955. Supra continued as a family managed company until 2002, when it was acquired by GE Security, a division of the General Electric Company.

Current Usage

Nowadays, the usage has extended to homeowners who want to keep a spare key somewhere different than under a doormat or flowerpot and holiday villa rentals.


There is a video on how to open and close a lockbox on YouTube – not sure why a video was needed but if you’ve never seen one in action then now is your chance!

Setting the Combination

The inside of the lock box lid has a cover which, when opened, exposes 10 screws corresponding to the numbered buttons on the keypad. The screws have arrows on them. A combination is set (or reset) by changing the direction of the arrows for numbers in the combination.

How secure are these boxes?

Well you probably think that the four-digit combination can be any number from 0000 to 9999. If it really was 9999 combinations that would be pretty good, as anyone attempting to gain entry to the lockbox, then the property, would have to spend quite a while pressing buttons and pulling on the metal cover – the whole mechanism is quite clunky and even when you know the combination the cover doesn’t always come off.

Sadly the combination can’t be 0000 as the setting inside the lock box lid only allows for one number between 0 and 9 to form part of the combination. So the first possible number is 0123. I guess you’re thinking, well that’s still a lot of numbers to try, even though you can skip 0131 as it has two 1s in it.

Unfortunately there is another design flaw in these boxes: The setting inside the lock box lid doesn’t allow you to choose the order in which the numbers should be entered. That means that if you tried 0123 then there is no need to try 1230, 2301, 3210 etc.

I sat and worked out the possible combinations for a lock box and there are only 161. I won’t publish the list here as it might fall into the wrong hands.
9th August update – I now have a formula to work out combinations and wrote about this in a newer post here.

So what should you do?

I’d recommend changing your lockbox to something more secure. I haven’t researched better options, but if there was something with six rows of rotating combination wheels, where each number could be anything, then I’d buy that. At least then you really would have a range of 000000 to 999999.

And what will I do?

I’m going to write to the lock box company and tell them my findings. My guess is that they already know, but keep selling the boxes anyway.