Back here at home a wakeup call from triple a. We have been warned about texting while driving. Now there's a new study about hands free devices and something called a kind of blindness behind the wheel which is where we find david kerley tonight. Reporter: So how many electrodes are you putting on? I am getting wired for research. I'm going to go ahead and stretch this over your head. Reporter: Maybe not a great look. I'm going to go ahead and put the chin strap on. Reporter: But all these connections -- go ahead and scan your eyes to the left and right as far as you can. Reporter: Will measure how much my brain can handle behind the wheel. Reaction time. Where my eyes look. Nine million cars today -- 62 million in five years -- will have systems that let you talk to your car so you can keep your hands on the wheel, but is it safer? 62 million in five years. Is it safer? With a small button on my thumb, I click when a green light flashes, simulating something on the road that needs my attention. I drive listening to the radio. Then another trip, with speech to text, hearing and answering email. Hey, I haven't heard from you in a while. Reporter: Reply. Okay, what would you like to say? I'll talk to you soon. Send. I clicked the button, but -- how did I do, joel? Your response times were a bit delayed when you are engaged in that speech to text task. Reporter: Here's what researchers for aaa found -- the least amount of distraction was the radio going up the scale, talking on a hands-free phone, talking to a passenger, a handheld phone was next. But it's those speech to text programs causing the most distraction. A fraction of a second. It can be dangerous. They call it, "inattention blindess." Even if your hands are on the wheel and your eyes are on the road, you may not be safe. Reporter: Automakers say the study sends a misleading message, suggesting hands-free and handheld devices are equally risky. The risk, says aaa, is that these systems sold as safe may really lead us -- Reporter: -- To distraction. Your next message is loading. Next a moment of terror 46

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Hands-Free Technology May Be Biggest Driving Distraction

ABC News' David Kerley helps test voice-activated gadgets designed to keep drivers' eyes on the road

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