I leave the door unlocked with the keys on the kitchen table. 

There was a police chase, car wreck, and one suspect ended up finding the unlocked door and locked themselves in the unit. 

Love finding deals and rehabbing/ unlocking value!

A rate increase (even if significant) seems like a small price to pay to unlock ~$127k in cash for additional investments....

They get two comfortable with me after a while and they lose their touch, thinking they can just unlock the door and collect a check on a property I did all the leg work on...Frankly I think your realtor is less important than having multiple realtors.

Good Article to inform owners, ThanksTerrible for the owner and how ever these people gained access makes you wonder.Protect your properties don't leave them unlocked or looking vacant. 

This is a general response, naming attributes, based on your post and what I would want personally:-Monitored, police response -motion sensors in appropriate areas-cameras both indoor (public areas)  & outdoors - motion activated, records to cloud, holds for minimum 48 hours, w/ audio capability-remote light switch control-remote alarm mode settings : on, off, at home-remote lock / unlock entrance-remote doorbell camera (service, delivery interaction)-temperature & flood sensors around appropiate areas-alert capability (various) set for your concerns-ample exterior motion dection led lighting, some solar powered lights that illuminate all night-phone app that you are comfortable usingThere are more attributes I would want but I'll stop here. 

My partner is positive that no windows or doors where left unlocked.  

And, that code could be entered into the device at the entry door which would unlock the door allowing access to their rental.

About a week after I bought the property the property manager called to tell me that the previous night one of the tenants became locked out due to a deadbolt lock that fell out when he tried to unlock it.