I took the SAT 4 times and the ACT 8 times... I think there were maybe 3 of those times total that the proctor actually looked up after reading the "calculator" instructions and peered around to see if we had appropriate calculators. There was only ONE time that I remember them actually going around and looking at everyone's calculators, and even then it was little more than a cursory glance.
Then again, they MIGHT be likely to take note if you were using a calculator you weren't supposed to have-- the ones with, say, printing capacities are noticeable, as are the ones with QWERTY keyboards. Other than that, any calculator unlike the ones most everyone else had would stand out. And, really, it's best to not risk it and just use an acceptable one. And I'm sure there are testing sites where the check more closely, that was just my experience; it would also depend on the individual proctor-- different proctors approach the test and the instructions differently.
If that's what you meant by "check"-- there was one girl on here saying that they actually cleared the memory of her calculator before she took the test! While I do think they're well within their rights to do that, I'd never heard even the suggestion that they would before-- and the theory is that the questions ask for REASONING, so even a better calculator or anything you have on it won't change your score too much. If you have something on your calculator you don't want erased, just in case you can ARCHIVE it so that the standard "RAM Cleared" won't get rid of it.