Research of Similar/Already-Existing Devices:

Some doors are self-locking
There are alarm systems, but they range in price from $300 per zone, to a flat rate of $2000.

As of yet we have not discovered a system to inform someone of a door being unlocked, although if an alarm were triggered during the middle of the night, that would be a definate indicator. Again, the only thing that comes close is an expensive alarm system which primarily charges for labor rather than parts.
There are systems that lock doors (securitech) and ones that lock doors at predetermined times. These doors can range in price and they get expensive fast. The actual lock doors are only from 30-50 dollars, but a predermined time can get as high as 100-200 dollars
- They may not have audio stimuli, and if they do, the added cost would be unnecessarily high because it is a special request, and even then the company would probably be unwilling to tailor a product to one person
We cannot alter the structure of the door, per the contract of the apartment

JCGResearchResults