How to activate voice wakeup in secure lockscreen on Samsung Galaxy S4?
I have not tried this myself, but it should be possible with tasker and (optionally) the Secure Settings addon – provided there's some automated way to let the device know you're in "driving mode". This could either be the car's Bluetooth (if any), or some NFC tag you place in your car to toggle that state (the latter could be used to toggle a custom variable or the "state").

With those pre-conditions met, setup your profile(s) corresponding to your "identifier". With Bluetooth:


Condition: Bluetooth device connected
Task: Turn off Keyguard


(will revert to the previous state, i.e. re-enable Keyguard, as soon as the condition is no longer met, i.e. your device no longer connected to the car). With NFC, slightly different, your Task should toggle Keyguard – so it turns it of on first read of the tag, and turns it back on when reading the tag again.

With Keyguard turned off, there's no pattern or PIN lock anymore, and the device should react as if you'd unlocked it. You can toggle Keyguard with Tasker itself; however, the Secure Settings addon gives you additional control. Check out what fits you best; above "pseudo-profile" should get you started :)