Yes, exactly. I used to design tools to test these and we weren’t allowed to patent them, but I think some of the high level concepts were secret patents though I can’t know that.

For anyone wondering the thing ICBMs (and jet planes) use is called a gyroscope and gives the same output but it isn’t a “spinning top” gyro that you might be thinking of. Rather think super sensitive dynamo, or reversed motor. Tiny rotation turns into voltage signal.

There is an even newer type that uses laser but I don’t know anything about it.