My maintenance guy knew the apartment was empty and went ahead and changed the locks to get the new key on the master system but left the door unlocked incase anyone came back.

Before unlocking the door turn and state.  

The click-together interlocking ones tend to stay straight and can be locked and unlocked.

I am unable to unlock cash in current portfolio in form of fixed second on current primary or heloc because of my DTI.

You can always sell it in one, five, ten years down the road if the equity you could unlock is hard to resist. 

There's several strategies you could take here, including unlocking some of that equity rather than outright selling. 

But then I could sell and unlock the other 30% of equity and move on.So basically what I'm looking at here is either 1) sell and give the IRS 40% of my profits and walk away with $40k (assuming the above sales price works out... it could very well NOT work out this way), OR 2) retain the house, rent it out at $0 cash flow per year, but get a $100k check in 5 months to go reinvest.Is my thought process correct here?

If this ends up working for you, please let me know.I'd recommend a kevo quickset smart lock with the kevo smart hub, which allows wifi access to the lock so you can lock/unlock the door from anywhere. eKey handoff is pretty simple with it as well.I haven't looked into the smart smoke detectors or water detectors, but I do like your thinking behind these devices.But from our findings, we've found millennial renters are willing to pay a 10-15% rent premium for smart home amenities, so I'd say its worth looking into to see how IoT devices can impact your bottom line.

@YiBing T.I use August, it’s phenomenal, you can administer virtual keys, can lock and unlock remotely, log of activity and it’s only the latch lock so no need to get new handles.

I'd certainly not do the auto pilot thing either.Any Realtor worth a flip shows a property and when they are done, checks the property to ensure it's locked up, that the back door wasn't left unlocked, etc.