We do not recommend that Quell be used while driving. The concern is that your leg could rest against either the center console or door depending on your position in the car and depress the button. If the button is depressed and you are not aware, the intensity could increase to an uncomfortable level or the device could even be prompted to calibrate. We are just concerned that both scenarios could increase the intensity to a very high level that could distract you from driving.
Newer Quell devices (serial #s start with 6) have a setting that enables you to disable the button. You can access this through the Settings menu on the Quell Relief app.