Hillsboro - Doug Woods wondered whether people taking his CPR classes were really getting it.

As a paramedic, he knew what it felt like to give someone the life-saving technique. He told those he trained about the tired wrists, fatigued arms and aching backs that come with correctly performing cardio-pulmonary resuscitation.

But he could never be sure that they would apply the right amount of pressure and get their timing right if faced with a real emergency.

About two years ago, Woods called the manufacturer of the mannequins he was using to see if they could build one that measured the depth and frequency of chest compressions.

"I just figured technology must have come along far enough by now to be able to do something like this," Woods said.

The Denmark-based company turned to a Los-Angeles based software company for advice. Computer software engineers in Australia and Hong Kong built a program to track a person's chest compressions, using the same technology as the popular video game Guitar Hero.

Woods developed a website that can tell someone whether they are performing CPR correctly as they pump the chest of the interactive mannequin. He also developed a presentation and written exam that can be taken over the Internet at any time.

The test, combined with scoring at least a 70 percent effective rate on the mannequin, qualifies someone to become CPR certified.

Woods, who spent seven years as a flight paramedic and now works for the Big River Ambulance District, recently introduced the technology to the freshman class at Hillsboro High School.

One by one, students knelt beside the mannequin and watched a computer screen to see if their compressions were working.

Each compression produced a color-coded bar on the screen. Red was too slow. Orange was too fast. Green was good.

Maria Wiseman, 14, of Festus, scored the highest with a 95 percent effective rate.

"It's a little more realistic," she said. "It made me feel more conscious as opposed to just the doll."

Woods says it builds "muscle memory."

But he also admits he's not the first to think of such technology. Computerized mannequins have been on the market for years. One, called Resusci Anne, produced a reading similar to an EKG that measured chest compressions.

But Woods said his invention is the first to provide real-time results that allow people to feel the difference between an effective chest compression or one that fails to do the job.