What is a good hardware solution that prevents me from forgetting to lock my office front door?

I'm an apartment manager and most days I'm the only employee on site. This means I'm in and out of the office constantly. I've been known to enter and exit 20 or more times a day. I truly need some kind of mechanism that prevents me from forgetting to lock the door.

First, install a closer. Second, install a Schlage A series, Arrow M series, or other quality lock that that can be set to re-lock itself whenever the door is closed.

Or, order a lock with a stockroom function. Those ALWAYS re-lock, and can't be set any other way.

If you can leave the door open while you are in the office get a vestibule lock this is one that you open with a key but stays locked when you close the door.You can unlock it if you want to but it will remain locked if you don't.

Why not add a "kickstand" to the office door and just make it so that the door always locks in the closed position?

This way, when you're in the office, you use the kickstand to keep the door open, and it also serves as a visual flag to whomever wants to see you that you're available. When you leave, you need to physically close the door and it automatically locks.

They make locks(doorlocks) that are self locking. Get one of those,but you'd better remember to have your keys with you!

just fit a five lever night latch it will lock as soon as the door is shut you have just got to remember your keys
or just put a note on the door