As a designer, you should be intelligent about where and how to use design and voice in a manner that anyone can use it, irrelevant to how they speak or how they listen. Saying something on your phone with a loud, busy train in the background is an example, why it’s necessary to recognise how different conditions influence the type of interface you designed. If the primary application is for driving, it is an excellent choice then – the hands and eyes of users are busy, but their voice and ears are not.
If you use the app somewhere in a noisy place, it’s better to request on a visual interface, for the surrounding noise makes voice recognition and hearing more challenging. If the usability of your app is both at home and on a public conveyance, it is essential to provide an option to switch between a voice and visual interface. In a normal conversation one to let another know, that he/she is interested in a conversation by nodding heads, smiling, and some other gestures. Similarly, it should be delivered to the users who interact with your machine. It’s essential to respect this with your design, so the user grasps their device is switched on and pays attention to them.