Yes, you understood that correctly. Cops can get a warrant to search, for example, your home for criminal activity that hasn't yet occurred. This insidious device is known as an "anticipatory search warrant."
Begin with the foundation: The Fourth Amendment to the United States Constitution prohibits "unreasonable searches and seizures," and provides that "no Warrants shall issue, but upon probable cause." This language is clear.
An anticipatory search warrant is a warrant based on a showing of probable cause that particular evidence of a crime will exist at a specific location in the future. In U.S. v. Grubbs, decided in March 2006, defines an anticipatory search warrant “a warrant based upon an affidavit showing probable cause that at some future time, but not presently, certain evidence of crime will be located at a specific place.” The Supreme Court had no problem with using anticipatory search warrants.
With a typical search warrant, officers requesting the search must establish probable cause that what they want to look for is presently in the place they want to look for it. If the government wants to get into your house, it needs to show probable cause the drugs are in the house. It doesn't have to be certain the drugs are there, but it must at least make a showing that they reasonably believe the illegal substance is there. In contrast, an anticipatory warrant doesn’t claim the evidence is in a particular place at the time the warrant is requested. Instead, that kind of a warrant anticipates a certain event will occur and if that event happens, then there is going to be probable cause.
Using U.S. v. Grubbs as an example, Mr. Grubbs ordered a child pornographic video tape from an internet site. Unfortunately for Mr. Grubbs, the site was being operated by the U.S. Postal Service. Agents intended to deliver the tape Mr. Grubbs ordered, but that delivery had not yet been made. The agents wanted to search Grubbs’ house after delivery of the tape to prove that he was in possession of it. The government wanted to get the warrant before the delivery so once the delivery was made, the agents could immediately conduct a search for the tape inside the house. In that affidavit they told the magistrate what they knew and they requested to execute a warrant to search for the tape if a triggering event occurred. The exact language that was in the warrant: “Execution of this search warrant will not occur unless and until the parcel has been received by a person and has been physically taken into the residence. At that time, and not before, this search warrant will be executed.” Delivery of the parcel and acceptance of the parcel was the triggering event. If the triggering event doesn’t occur,the warrant can’t be executed.
What's to stop the government from fabricating an event, placing any person in possession of an illegal item or substance, then executing upon a warrant for the mere purpose of getting into your house?