Yeah, I could probably leave without suspicion for an hour or two, but it depends on the day.
I'm to the point where I'm popping in and out of the engineering office fairly often now, visiting our other sites to make use of their unique equipment and personell, visiting customer locations, purchasing new supplies, or else just out in the shop working on various projects.
Someone would definitely notice before the day was done, and let's just say, there would be a substantial and immediate removal of privileges, and devastation of trust.
Plus, I have no desire to do that; I do rather like my job. (Except for the 8am start time.)