When Lovers' Quarrels Go Hi-Tech

March 19, 2009— -- For a year, he just didn't seem the same. He wasn't where he said he'd be. He hinted that he was leaving. He said he wanted a break.

So, Michelle (who spoke with ABCNews.com on the condition of anonymity) spent $1,500 on a GPS tracking system to test her theory that her husband was having an affair.

The technology confirmed Michelle's mounting suspicion: Her husband of 14 years was seeing another woman.

"Spying could seem extreme [but] once you get to that point, you already know. It's more of a closure thing," she said. "I was blaming myself. I was turning into a state of depression. ... I know now that he's the jerk."

As surveillance technology, such as GPS tracking devices and video cameras, has evolved to become smaller and cheaper, more and more people like Michelle are turning to spy gadgetry to not just monitor their property, but the people in their lives.

But, experts warn that it's easy to cross the line. Stalking is illegal, and depending on your state, you could find yourself running afoul of the law without even knowing it.

Earlier this month, the New York Post reported that former football player Michael Strahan installed a tracking device on his girlfriend's car when he suspected that she was cheating on him.

Nicole Murphy, the ex-Giant's girlfriend, reportedly discovered the device behind the front dashboard when she took her Range Rover to the dealership.

But people in the industry say Strahan is hardly alone in using sophisticated spy technology for personal purposes.

"Even in this economy, our business continues to grow," George Karonis, president of LiveViewGPS, told ABCNews.com.

Karonis sells a wide range of commercial-grade GPS tracking systems online and, though he would not disclose details, said "sales are brisk."

Most of the company's clients are businesses that use the devices to track delivery trucks or other mobile employees, but he said 40 percent of customers are individuals who want to recover stolen vehicles or monitor teen drivers, older family members or cheating spouses.

The company requires that all clients sign an agreement stating that they do not intend to use the technology for illegal purposes, such as stalking, Karonis said.

But he acknowledged that once the technology is out of the company's hands and activated, it can't monitor what its clients do.

"Truth is what people seek and are willing to pay any price to find -- or a reasonable price," Karonis said. This is "something that verifies the truth."