How to prevent students from using modified calculators to cheat on exams?
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.