Though the earth and all inferior creatures be common to all men, yet every man has a "property" in his own "person." This nobody has any right to but himself. -John Locke's Second Treatise on GovernmentBy extension, you have a natural right to "privacy" that can only be alienated if you infringe on the natural right of another's person or property:
The only right “to privacy” is the right to protect one’s property from being invaded by someone else. In brief, no one has the right to burgle someone else’s home, or to wiretap someone’s phone lines. Wiretapping is properly a crime not because of some vague and woolly “invasion of a ‘right to privacy’,” but because it is an invasion of the property right of the person being wiretapped. - Murray Rothbard's The Ethics of Liberty
Like a wiretap, the TSA scanners (and much else about airport security theater) are an invasion of your property rights.