Remove all, change the locks, maybe install a camera or two just in case, and done.

Of course this was a "grow house", so...4 - High end (very) security system (cameras). 

Security cameras to catch visitors.

You also see it a lot with individuals hiring house cleaners, gardeners or nannies.

However if they and security cameras become ubiquitous, agents are likely to get displaced.

I did swing by and install my new ReoLink security camera.

Next time I buy an old house, I'm definitely doing a sewage line inspection with a plumber and a camera. 

It has a color touchscreen which is simple for guests to operate.I also have 2 Digital Watchdog exterior cameras so I can keep an eye on who is coming and going and monitor when the house is between occupants.

Let’s face it, property management is mostly just scheduling, which anyone can do from anywhere on the planetMy offshore PMs set door codes, message & call guests, schedule cleaners, adjust the thermostat, monitor my cameras, call plumbers and more!

Pumping the tank when it needs it and running a camera through the lines are the best line of defense.