I don't have a door that locks anywhere in my home. Not even to the outside.
Where I live (Canada) there is a similar deduction for a home office but no requirement about having a locking door. That would simple be unenforceable, since tax auditors have no right to enter your home to ensure deduction guidelines are being followed.
We do, however, have a mountain of paperwork to file for both you and your employer to vouch that working from home is a necessary part of the job, and you have to be swear that that portion of your home you claim is not used for non-work activities more that some small amount of time. My estimate was around 5% of my home.
I suspect there are going to be fireworks in the near future as tax legislation changes are debated, with the never-homers trying to quash the forward-thinkers and their changes to the system. I also foresee insurance companies jumping in to take their cut.