Strange HP on eBay


Can any of you identify this device?

It is from eBay auction #5787103394.


I used to work for HP and remember these things, They are basically a security device to prevent anyone walking off with your calculator.


So it is a (then) standard calc, just secured inside a special cradle?

What type of calculator is it?


IMHO, it looks like a HP-21 in a theft protection device.
I remember these had a thick steel cable. No problem for
a bolt cutter, though. Vendor should offer the key, too,
otherwise you can't get out the HP-21 undamaged except
if paying a locksmith (who might cost you more than the
HP-21 is worth).


Here's an old picture I took that I never got around to adding to the museum.


Yup, we used to have these contraptions bolted to the lab bench top in physics class years ago in college. They were purchased by a far-thinking professor who wanted the best tools possible for the class. However, the calcs were always dead because it was such a hassle to find the key and change the batteries.

Sadly, the TI's that were commonly available at the time I took the class were far cheaper and equal in function compared to the HP's in the security case by the time I got there.

To their credit, they were durable though.

Calcs in general were unique and much more valuable then.


When I was in high school, our chemistry lab had TI SR-10s bolted down like this. There was a "calculating station" with four of them - at standing height so you didn't get too comfortable and waste time with a precious resource. (The resource being essentially a 6 function calculator.)

Of course, an inflation calculator does say that they cost about $660 USD in today's dollars so I guess that was worth protecting.


The Woodstock series security cradle also had an additional 'lens' over the display that helped bend the display output. This helped to move the useable viewing angle closer to the keyboard and more suitable for use on the desktop. I'm not sure it was all that effective. The cradle certainly did make a pretty tough calculator nearly indestructible.


(1st time poster, former HP'er (although not in calculators), and PPC member #7042)



On my website you can see all (?) security cradles/cables for different HP calculator models:


So, how do you break in to one? (This one is missing the key, according to the auction.)


Hi Howard et al,

Somebody kindly sold me an Hp-29C in a security device without key.

With my Dremel & a 9911 tungsten Carbide tool, I've drilled 5 holes in the lock (domino style) then tool 545 cutting between holes.

It works fine except that the lock is not intact anymore (just "Near Mint" for Ebay ;-).

Best regards



The locks are relatively easy to pick. I obtained one with a cable that was locked with no key, and one without a cable that had two keys. It was easier than I expected to combine the keyed cradle with the cable. The unkeyed one was relegated to storage, as I didn't want rely on my amateur locksmithing skills to get a calculator out of it.



I saw one of these in the 80's. I'm not sure if it can hold anything but a Woodstock.

At that time, the owner had the cradle and an HP29C, fortunately outside it, but he had no idea of where it was the key to open the security lock (the cradle was locked). The owner asked me for help, and I knew about one of the best 'key makers' (is it correct?) in the town.

I saw the man furiously trying for about half an hour to open the cradle with his tools. Finally, he gave up and told me: 'After more than 30 years, this is the second time I cannot open a custom lock'. The poor man was desolated.

The calculator in your picture is surely an HP21, the only Woodstock with a single shift key injected in blue. The HP21 had no inscriptions in the keyboard faceplate, only in the keys (slanted face).

I hope the buyer succeed opening it without destroying the cradle... or (worst) the calculator 8^(

Best regards.

Luiz (Brazil)

Edited: 5 July 2005, 5:59 p.m.


That is a great story! The unbreakable lock
fits in with the whole HP calculator ethos perfectly.


In my experience the locks on the HP security cradles are not difficult to pick. They are normal pin-tumbler cylinder locks and there are no spool pins or anything like that.

If the cradle is not fixed to anything, you can insert a finger through the hole in the back to apply torque to the locking mechanism in the 'opening' direction. Then just pick the pins as normal.



And here I thought we'd run across another piece of the HP calculator legend.

On the other hand, if I win the darned auction, there's some hope I can rescue both the cradle and the calculator. 8)


...and, thus the reason for them ALWAYS having dead batteries in them !

We could never find the keys, so they were like little museums holding one example of an HP.

...I wonder what happened to them. They were still bolted in place 5 years ago when I visited my old college?


Hi, Tony;

I do not recall it precisely (it was probably 1989 or 1990) but I remember that the cradle was empty, no calculator on it, and I could not even see the locking 'tab', neither how were the top and botton halves kept together. Is it possible that different versions of the security cradle exist and at least one of them does not allow it to be openned without the keys? Just curious about it.

Thanks for the additional info.

Best regards.

Luiz (Brazil)


Hi Luiz,

Echoing your post, the Woodstock craddle I got also had a recessed lock.

That's why I resorted to virile brute force to free the calc (see my upper post)!

BTW thanks for your kind mail!

Best regards



I heard a case, at a university back in the 70s where a whole table top was removed from a table in order to steal a calculator in one of these cradles.

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