What is the current state of the law in the US when it comes to electronic surveillance?

The necessity of protecting individuals from unjustified state intrusions is well recognized and was expressed in Hunter v. Southam as: …That purpose is, as I have said, to protect individuals from unjustified state intrusions upon their privacy. That purpose requires a means of preventing unjustified searches before they happen, not simply of determining, after the fact, whether they ought to have occurred in the first place. This, in my view, can only be accomplished by a system of prior authorization, not one of subsequent validation.[9]