Sen. Charles Schumer wants the federal law against stalking tightened to stop someone from slapping a GPS tracker on the car of a target, such as victims of domestic violence.

GPS technology that is becoming more commonplace has made devices easy to get, and cheap, too, with retail prices of a few hundred dollars. They are also small and hard to spot if hidden on a car.

"It's amazing -- police officers, to track you, the Supreme Court has ruled, need a warrant," Schumer said. "But any other citizen for whatever reason can put a tracking device on your car."

Schumer's bill would make it illegal for someone to do that with the intent to run surveillance on another person without their consent.

To highlight the loophole that exists in federal law, Schumer recounted the 2012 slaying of a Buffalo woman, Jackie Wisniewski, who was killed by an ex-boyfriend after local law enforcement could do nothing about the GPS tracker she found on her car.

Exceptions in Schumer's law include police with a warrant, parents of minors and employers who inform workers of the tracking while on the clock.

Schumer cited a 2012 New York Times report that pegged the number of GPS devices sold to private individuals at 100,000. "You can be sure tens of thousands already are being used this way," Schumer said.