Lee Little got the idea for his startup during a frustrating visit to Yellowstone National Park six years ago.

"I had a lot of questions, like why do some geysers go shooting up and some just bubble up, but I couldn't find a park ranger anywhere," said Little, who was a sales director at Advanced Micro Devices Inc. at the time. "It got me thinking how you could use technology to really improve the experience."

The result is GPS Ranger, a portable handheld device that uses global positioning technology and multimedia content to provide educational self-guided tours.

Little's three-year-old company, Bar Z

Adventures, has installed the systems at six national parks and zoos, including Death Valley National Park, Vicksburg National Military Park in Mississippi and the San Francisco Zoo.

"It's like having a history channel on the palm of your hand," Little said. "Park rangers are amazing fountains of knowledge, if you can find them. We're helping visitors connect with the experts and leave with a fuller experience."

Death Valley, which receives 850,000 visitors annually, launched the service in September. Visitors pay $19.95 to rent the device, which they fix to the dashboard of their car and use to navigate the 3,000-square-mile park.

When drivers approach a landmark, the device, triggered by the GPS system, offers video commentary by a park ranger as well as vintage photos and audio and video clips.

At some areas in mining ghost towns, visitors can take the device out of their car and walk around the sites while listening to detailed descriptions of what they're seeing.

"With the volume of people coming through our park, it's impossible for us to be everywhere," said Terry Baldino, chief of interpretation at the park. "This really enhances the experience. The folks I've had a chance to chat with love it."

At the San Francisco Zoo, users can take behind-the-scenes video tours of 25 exhibits, watch animals interact with their keepers and observe behavior training sessions. The device includes maps and trivia quizzes.

Bar Z's competition is limited. Though some companies offer cell phone and iPod guided tours of indoor venues, such as museums, GPS-guided tours of large sites are rare.

Bar Z — which is named in honor of Little's grandfather, a South Texas rancher who bred Barzee Brahman bulls — is funded by Little's family and two private investors.

The cost of GPS Ranger varies depending on size. A 50-unit installation, the size of the San Francisco Zoo's project, includes hardware, software, content, installation and training, and costs about $75,000.

Customers usually rent the system over 36 months. A 50-unit project would require about eight to 10 rentals per day to break even.

The San Francisco Zoo's GPS program has exceeded that goal and is now making money, Little said.

Bar Z gets revenue three ways: on the initial installation, through a percentage of each rental and on location-based advertising. Dippin' Dots Inc., for example, is an advertiser at the San Francisco Zoo. Bar Z, which is focused on expansion, is not yet profitable, Little said.

Bar Z runs the back-end system and provides parks and advertisers with data on visitor traffic, such as how much time they're spending at each attraction. It can change rental pricing depending on attendance and can alter content for special events.

With attendance at national parks and major zoos on the rise and budget cuts reducing staff sizes, Little believes the demand for self-guided tours will grow.

"People arrive really wanting to learn, and often they walk around a few hours and leave with no real knowledge of the place," Little said. "We want to help change that, and we really believe that the visitors do, too."

lhawkins@statesman.com; 912-5955