No part states it explicitly (such technology didn't exist when it was written). People who are arguing against this practice cite the 4th amendment, which reads as follows:
"The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."
People are arguing that putting a tracking device on a car constitutes a search.
"The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."
People are arguing that putting a tracking device on a car constitutes a search.