I learned to drive a semi truck when paper logs were how you managed your driving hours. I don't want to suggest that any truck driver would falsify a paper logbook, but I am sure pages were lost and had to be replaced. One of the things a good friend suggested, was to carry a rock. A small one that would fit in the palm of your hand, but big enough that your fingers would barely close around it. Small enough that it didn't affect my driving, but large enough that if I got drossy it would slip thru my fingers and find the floor. Back in those days, all we had for floors was the steel cab floor. If you dropped a rock in the confines of a truck with steel floors, the noise would be loud.
I don't know well a rock would do in the plastic drivers compartments with all the sound proofing such as padding and carpet, but I kept that rock in my hand for many years, turning it around, just flipping it over and over while I drove. I lost that rock when I changed trucks one time, but I remember that it had been worn smooth from my handling it.
Maybe a rock is in some of you guys' future? Make it and oddball shape and not too small. Keep it in your hand anytime you get in a vehicle, driving or not till it becomes a habit like putting on a seatbelt or putting the keys in the ignition. Make sure it is big enough to make a noise. I know when my rock would hit the floor in that truck, it would wake me up, no... it would scare me!
David from Jax