But the satellite navigation that allows for such tasks also helps police track a phone user's exact location, and Texas civil liberties advocates say that kind of surveillance without court approval goes too far.
They want to update state law to require a court-ordered warrant for cellphone GPS tracking by law officers, with some exceptions. Police can currently track someone's whereabouts by requesting cellphone company records, said Scott Henson, whose Austin-based gritsforbreakfast.org is influential among criminal-justice policy watchers.
"The law has not kept up with the technology," said Henson, who is circulating proposed legislation to modernize the state Code of Criminal Procedure. No lawmaker has agreed to sponsor the measure yet, he said, but "folks really seem to intuitively understand that it's a big deal."
The American Civil Liberties Union of Texas and EFF-Austin, a "cyber liberties" organization, are also working on the effort, part of a national movement toward tightening up privacy for mobile device users.
Texas law officers currently have to get a court warrant for a wiretap, Henson said, and a court order is required before police can attach an electronic tracking device to someone's vehicle. But he said the rise of smartphones equipped with GPS navigation means police can simply subpoena tracking records from cellphone companies, which received 1.3 million such requests in 2011.
New technology, apps and information-sharing among federal, state and local law enforcement provide additional ways to get the data, said Matt Simpson, a policy strategist with the ACLU of Texas.
"We want to make sure there's a ground floor that no one could sink below in protecting constitutional rights and privacy," Simpson said.
While police respect privacy rights, law enforcement uses technology to combat crime, just as criminals use it for their purposes, said Charley Wilkison, public affairs director for the Combined Law Enforcement Associations of Texas.
"It's a balance between the freedom of the individual ... and the right of law enforcement to try to get at the bad actors," he said.
Wilkison said accusations that GPS data is used broadly by police to spy on regular citizens are "a damn lie." But he acknowledged that civil liberties advocates have a receptive audience among many lawmakers because of the "strong libertine, independent streak" in Texas.
Other parts of the proposed legislation would allow a judge's order for location tracking to be sealed only for 180 days, not permanently. The legislation would require state law enforcement to report on the amount, type and outcome of location tracking by police agencies, similar to other aggregate law enforcement reporting.
The Freedom of Information Foundation of Texas could find that public reporting aspect of the proposal appealing, though it would need to see the filed bill before expressing support, said attorney Laura Prather, co-chair of the foundation's legislative committee.
"We're about transparency and having checks and balances on the system," Prather said.
How police officers must obtain cellphone tracking information has not been fully answered by the courts, said Richard Segura, a supervising attorney and skills director for the criminal defense clinic at the University of Texas School of Law.
Cellphone location information and a "star witness" from a cellphone company helped to convict a capital murder defendant that he represented several years ago, Segura said. Red dots shown on a screen in court tracked the defendant's whereabouts, and the defendant ended up with a life sentence.
"Literally, he left an electronic paper trail" using his cellphone, Segura said. "They literally drew a map from the death scene to his apartment."
It's clear that many people view their phone conversations and phone activities as a private matter, Segura said, suggesting that lawmakers do as well.
"Do the legislators really want the public to know that their vehicle stops by the bar on the way home every day?" he said.
License plate scanners, like those Dallas police will soon use, show there are multiple electronic ways for law enforcement to check on citizens, said Simpson of the ACLU of Texas.
Henson noted that the proposed legislation narrowly focuses on GPS navigation data and doesn't address other apps or technology, like those that allow people to listen in on others' conversations via smartphones.
"We're trying to open the door," he said, "and say let's at least take the first step through."