That’s according to new research by the American Automobiles Association’s Foundation for Traffic Safety which found that mental distractions can persist long after completing a task.

The researchers compared new hands-free technologies in 10 2015 vehicles in the US and three types of smart phones. The analysis found that all systems studied increased mental distraction to potentially unsafe levels. The systems that performed best generally had fewer errors, required less time on task and were relatively easy to use.

Researchers found that potentially unsafe levels of mental distraction can last for as long as 27 seconds after completing a distracting task in the worst-performing systems studied. At the 25mph speed limit in the study, drivers travelled the length of nearly three football fields during this time. When using the least distracting systems, drivers remained impaired for more than 15 seconds after completing a task.

“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.”

“The massive increase in voice-activated technologies in cars and phones represents a growing safety problem for drivers,” continued Marshall Doney, AAA’s president and CEO. “We are concerned that these new systems may invite driver distraction, even as overwhelming scientific evidence concludes that hands-free is not risk free.”