From time to time, my dad (who lives where I invest) will go to a property to meet with a tradesman, unlock a door or perform a random task (like empty the coin op washer/dryer).

When I first started in Ohio I had my Realtor call the MLS and he said they unlocked a whole bunch of searches and said they don't let everyone do it.The only reason I do zips to start is when I go into a new market it helps me group where all the cash solds are.

She had to add a door and keep it unlocked to satisfy the city.  

Crime is largely either low-level property crime (I left my car doors unlocked and someone stole change) or "business disputes" of various street-level issues. 

The HVAC guy gave me a few options:1) Bare Bones $5000 - It will keep the place cool for roughly 8 years2) "Old Reliable" $7,500 - It cools, and is known for 15+ year life and a 10 year warranty3) Bells & Whistles $10,000 - High efficiency (we won't pay the electricity on this place), Variable speed comfort (it basically can adjust how much air it blows so that your house is at a constant temperature), can be connected with the "smart home" system so I can change the temperature or lock/unlock the door from my smartphone, have security cameras, connect the smoke detector etc.

Not accounting for missing numbers, though, (I sure wish I could unlock THAT mystery!)  

The front door is unlocked, and I loudly announce myself when I enter.

To simply allowing anyone to go in with the lockbox code is similar to leaving the door unlocked...Yes, like @Ryan D. sometimes I get into the houses without agent having to show me (wouldn't be necessary anyway).  

Heed the warnings (and opportunities) of those like @Arlen Chou that voice the risks - and what you can unlock.

I'm trying to unlock some of the equity in that home to help purchase future properties.