Hands on the wheel and eyes on the road? You could still be distracted while driving.  Voice-recognition software that many automakers tout as a safer alternative to handheld devices can still divert drivers’ attention, according to a new study published by AAA found.

Researchers noted that workload ratings were the highest on their scales when participants in the study used Siri.

The technology is alluring because it allows drivers to do things like change the radio station or compose a text message without removing their hands from the wheel or their gaze from the road. But many of those tasks increase a driver’s cognitive workload. Depending on the situation, that can be dangerous.

“It’s especially problematic, because you can be distracted and not know it,” J. Peter Kissinger, president of the AAA Foundation for Traffic Safety, told Autoblog. “That’s the nature of mental distraction. It’s hard to appreciate. … Often, you don’t know you’re distracted until it’s too late.”

There’s significant variation in the results of the study. Simple, single-task car commands for operations like changing the radio station caused minimal increases in workload, about the same as listening to an audio book. Composing information using speech-to-text technology was more burdensome, and using menu-based functions caused a high level of cognitive workload.

Siri-based interactions posed the highest levels of distraction, according to AAA. Researchers noted that workload ratings were the highest on their scales when participants in the study used Siri, and two of the three simulator crashes they observed during the study of 36 participants came while the subjects were interacting with Siri. The subjects weren’t looking at nor making contact with their iPhones during these interactions.