Our NICU is locked - there is literally no entrance without the electronic keypad entry. There is one entry for visitors. They call in from the hall and identify who they are and who they are there to see. We buzz them in - unless the baby is having a procedure or we are admitting to the next bed, or something like that, or - of course - if it is not within visiting hours. We do close the unit for 3 hours at each shift change to allow for nurses report and walking rounds with the docs, as well as AM labs to get drawn, other procedures done, etc. Otherwise we would have nosy parents there listening to report on every baby in the unit and others pitching a fit because their baby's heel was getting stuck, etc.
Our lockdown system is very efficient and effective. The only problems we have are with parents and visitors that hang around the unit entrances and try to see the nurses punch in the door code!!

I mean, why on earth??? If you have any business at all being in the unit, call in during visiting hours and we will let you in. If you go letting yourself in (like no one will notice?

) - we will call security and you may get your butt banned from the premises. If you don't belong in the unit to start with, we will call the real cops and have you arrested. Whenever this would happen and we would find out that someone knew the code, we would just change it. Did they really expect otherwise?? Duh!
Ah, visitors.