How to prevent students from using modified calculators to cheat on exams? Recently my faculty (mathematics and statistics) and I have been dealing with widespread cheating due to calculators that have been modified so as to have more functionality than is permitted.

At my university we have a standardized calculator that is to be used for tests. This brand of calculator has limited functionality however recently these calculators have been modified and sold so that students can cheat on tests. We have managed to get a hold of one of them and it appears that the electronics inside have been modified. We have managed to identify the group of individuals responsible for modifying and selling these calculators however we are not sure what to do about it.

Here are the options we have considered so far:


Check each calculator individually before tests to see if it has been modified.
This is impractical as they don't look any different on the exterior and are no different in weight. We would need to open them all up and look inside.
Provide our own calculators to the students.
This approach, although better than the last, has its drawbacks. It would be expensive for the department to purchase enough calculators initially and then they would over time break and be lost, resulting in more cost so we would prefer not to go this route for that reason. Additionally, students could still quite easily take a modified calculator of their own into exams and swap it out for the provided one.
Change the official calculator model.
We could move to a new model of calculator however I suspect this would only be a temporary fix as the group responsible for modifying and selling the calculators could easily switch to modifying the new model.
Stop having calculators all together.
We would prefer not to resort to this as we don't think forcing students to do lengthy arithmetic calculations is the best way to test them. We could try to avoid such things however sometimes it is simply necessary to ask such questions, for example, in an introductory stats class we would like to ask students to find the standard deviation of a set of data points. Asking them to do this without a calculator seems unfair however we can't simply avoid asking such questions if we want to test the students properly.
Taking action against the group responsible for making the calculators.
Fortunately this group has been identified, however they are not students at my university so we cannot take direct action against them for academic disintegrity. We would like to take legal action against them if possible however my faculty and I are unsure if there is precedent for such a thing. As far as I can tell they are not committing any crimes. If there is something we could do in this regard please let me know.
Simply ignore the problem.
This is obviously not ideal as using these calculators gives students a clear advantage over those without them. Additionally, students using them often don't need to learn how to perform various calculations and can instead just plug in the various values and have the answer come out.


Has anyone has this happen at their institution before? If you have any suggestions as to what we can do in this situation it would be greatly appreciated.



Here is some clarification on the exact nature of the modifications:
To enter into the modified "mode" you type in a sequence of numbers (eg: 1234567) then it enters into the new mode in which you can do many advanced calculations.
pressing the reset button on the back causes it to appear to reset without actually resetting. If you type the password in you will still get back to the modified mode. In this mode formulas can be saved for example.
I received my bachelor's degree in mathematics in 1970. I didn't own a calculator.

There were some adjustments that helped with no-calculator tests:


Many of my exams had ten points per question. 9 of the points were for clearly showing correct working. One point was for getting the right answer. A student who understood the material but was bad at arithmetic could get 90% without a single correct answer. A student who depended on a fancy calculator could miss more points for not showing all their work.
The exam booklet included, at the back, any trig and similar tables we were going to need. Answers only had to be to the rather low precision supported by those tables.
Questions were designed with easy numbers. For example, fractions would often simplify by just crossing out common factors.
Questions were structured to minimize difficult arithmetic. For example, ask for the variance rather than the standard deviation, but also ask what they would have done differently to get the standard deviation.


Given the problem of the modified calculators, you can go in one of two directions. The first is real world. Full Internet access, statistical calculators etc. The other is to go back to the 1960's, and design tests for no calculators.