You should be OK. I bet the screeners will notice them on x-ray and probably perform a hand-check of the carry-on bag they're in. I would NOT put them in a checked bag, for reasons of both potential theft and data integrity (the x-rays used on checked bags are much stronger and have a very small chance of damaging the drive's data).

The screener may not recognize the hard drive during a hand-check, but a simple explanation should suffice. I've traveled with external drives before--not with the bare drives you refer to, though--and have never had to even explain them.