Across the U.S., the general rule of law is that an individual has no right to privacy in public places. "If you're in public, you're in public," Dayanim said, and not protected as you would be in your own home.
But even then there is some flexibility for legal action. "You could have different claims depending on how someone used the information they collected in public," he said. "If someone took a photograph of you passing a gentleman's club and used it to portray that you went into the club, you could have the right to legal action because you may have just been walking by."
You wouldn't legally have the right to do surveillance or listen in to private conversations involving another adult, such as a spouse or lover, outside your home, but such actions would likely be permissible if you performed them while looking into the activities of your own child, if he or she is under 18, he said. As a parent, "you have the right to his or her personal information."
The same wouldn't be true if you were trying to check into someone else's child, he said. "There would be a variety of laws that would protect another child's privacy ... if you were trying to access their personal information."
What if you collect information about someone else using a GPS data logger so you can see where they've traveled and when they were in various locations? "I don't think that's a settled area yet," he said. "On one hand, your public movements are not private. You're driving around. On other hand, there could be a trespassing or other kind of [lawsuit]."
Keeping up with the technology
Scott Burns, the executive director of the National District Attorneys Association in Alexandria, Va., said new kinds of personal technology devices are sprouting so quickly that they're creating new challenges for state and federal courts.
"As a broad observation, I would say that the courts have not kept up with the technology and in many states the laws have not kept up with the technology," said Burns, who served as a district attorney for 16 years in Iron County, Utah, and as director of the U.S. Office of National Drug Control Policy for seven years. "I predict that we will see more litigation and legislation regarding the technology."
What that means, he said, is that there is still much interpretation to be developed about these kinds of equipment, how they are used and whom they are used by. "In my conversations with DAs and law enforcement officials across the country, each case would be analyzed on the specific facts, the equipment used and the relationships between the parties," Burns said. Much depends on whether there was consent for the use of the devices and if they were used in a home, business or public place, he said, and added that it's probably reasonable for someone to use such devices inside a property that they own, without the consent of others.
"I don't know if anyone would have a great case against you if you were putting a tracking device on your eight-year-old to be sure they were safely getting home from school," Burns said, but it wouldn't likely be legitimate if you did the same thing to one of their friends. "It's probably not a problem putting a GPS tracker in a vehicle that you own, even if it's used by a spouse or your child. But you may have a [legal] problem putting a tracking device on the vehicle of someone else," such as a boyfriend of girlfriend.
"A lot of that is premised on the underlying Fourth Amendment protection" of the U.S. Constitution, which provides a reasonable expectation of privacy, Burns said.
So how do you know when you're using security technology in an appropriate way?
"I am reminded of the U.S. Supreme Court justice [Potter Stewart] who once said that he didn't know how to define pornography, but he knew it when he saw it," Burns said. It's similar with personal security technology devices today, he added. "With respect to the use of this technology in the private sector, there are times when it is appropriate with family members. But there are times when it clearly crosses the line."
Todd R. Weiss is an award-winning technology journalist who wrote for Computerworld.com from 2000 through 2008. He's now a freelance writer, covering technology news, cool tech gear, open source and more. Follow him on Twitter at http://www.twitter.com/TechManTalking.
This story, "Personal Spy Gear: Is It Ethical? Is It Legal?" was originally published by Computerworld.