Hands-free technologies were designed to help keep drivers safe, but it could still be a distraction.

A recent study conducted by the AAA Foundation for Traffic Safety has found that potentially unsafe mental distractions can persist for as long as 27 seconds after dialing, changing music or sending a text using voice commands. The study shows that new hands-free technologies can mentally distract drivers even if their eyes are on the road and their hands are on the steering wheel.

In the case of a 27-second long distraction, drivers going 25 mph could travel the length of nearly three football fields in that time. When using the least distracting systems, drivers were still impaired for more than 15 seconds after completing a task.

To determine these results, researchers compared new hands-free technologies in 10 vehicles from the 2015 model year along with three types of smartphones. All the systems studied showed increased mental distraction to potentially unsafe levels.

The best-performing system was in the Chevrolet Equinox, having a cognitive distraction rating of 2.4. The worst-performing system was found in the Mazda6, scoring a cognitive distraction rating of 4.6. Among smartphones, Google Now performed the best with a distraction rating of 3.0 while Apple Siri scored 3.4 and Microsoft’s Cortana was worst with a 3.8 rating.

“The lasting effects of mental distraction pose a hidden and pervasive danger that would likely come as a surprise to most drivers,” said Peter Kissinger, president and CEO of the AAA Foundation for Traffic Safety. “The results indicate that motorists could miss stop signs, pedestrians and other vehicles while the mind is readjusting to the task of driving.”

This article originally appeared at AutoGuide.com