Cellphone location reportedly can be tracked even if the phone is powered off; and there is Stingray; the warrantless use of which has been allowed as not violative of the Fourth Amendment, by at least one trial court.
Privacy?
If the founding fathers had planned the Revolution by Internet, we'd all still be singing God Save the Queen. That is how it is, although we may feel it is not as it should be.
Yes, the allowed warrantless Stingray tracking was used against an identity thief, a bad guy, but privacy protection under Fourth Amendment precedent is almost always litigated in criminal proceedings, and criminals generally are not the most well mannered members of society. Indeed, many of the well mannered Wall Street criminals seldom are part of precedent, because they seldom are prosecuted, and if so, a deal gets cut where the firm and not the instigating individual fesses up and pays the government money with nobody sent to the slammer. Or culpability often is left hanging to avoid consequent civil litigation, a settlement without admission of guilt being fashioned, and the deal is struck that way.
Deal made, no appeal, no precedent. Smooth.