Although hands-free devices are supposed to help drivers not hinder them, a report from the AAA Foundation for Traffic Safety says otherwise. Some devices drivers use “may actually increase mental distraction,” the study’s authors found.

The findings undermine a key sales pitch used by car and app makers for voice-controlled technology. It also shows that drivers may be putting themselves and others in danger while they dictate messages, ask for directions and ask questions while trying to stay focused on the road.

Results of the study built off another in 2013 conducted with the help of University of Utah researchers. It used test vehicles, heart-rate monitors and other equipment to measure driver reaction times. In many cases, drivers using voice activated apps performed more poorly on the road than those who didn’t have them.

Voice-activated email features proved to be the most distracting, the study found. Hands-free phone calls were described as moderately distracting.

“We already know that drivers can miss stop signs, pedestrians and other cars while using voice technologies because their minds are not fully focused on the road ahead,” said AAA Chief Executive Officer Bob Darbelnet in a statement.

Researchers also looked at the impact of Siri, Apple’s (AAPL) voice activated assistant, and found that it “generated a relatively high category” of mental distraction.

But the AAA’s recommendations seemed particularly vague. The organization said the results broadly “suggest that developers can improve the safety of their products by making them less complicated, more accurate and generally easier to use.”

In the meantime, AAA encouraged drivers to “minimize” use of voice-based tech while driving. The organization is also meeting with policy makers to “ensure” that the technologies don’t “compromise” public safety. AAA did not advocate a ban on voice activated technology in the car. Using phone handsets while driving is, of course, already illegal in a number of states.

“It is clear that not all voice systems are created equal, and today’s imperfect systems can lead to driver distraction,” Darbelnet said. “AAA is confident that it will be possible to make safer systems in the future.”

If only Google’s (GOOG) self-driving cars were a commercial reality today.