If you cook for cops or give them some hot cocoa on a cold winters day they will monitor your property more. 

I am currently in the process to buy my 4th house bank financed and all of the sudden a property, that I was monitoring for a while, becomes available.

There are few services like the one you mention that are popping up which would certainly be an extra way of monitoring.  

Because you get automatic alerts to your phone if it gets too loud (and you can set hours & noise levels), it's a lot easier to monitor than a camera system. 

Do you charge for monitoring and maintaining vacant units?

Bigger Pockets has some great state forums and usually there are good locals that monitor those.

I'm wondering what system you'd  recommend for remote monitoring and security for the units?

Best thing to do is to monitor it.

- While home prices have risen for 97 consecutive months, July’s record-low mortgage rates have made purchasing the average-priced home the most affordable it’s been since 2016- Buying power for those shopping for a home is up 10% year over year, with home buyers able to afford nearly $32,000 more home than they could have 1 year ago while keeping their monthly payment the same- Each of the 25 largest markets are seeing their strongest affordability in more than 2 years, with falling 30-year rates elevating buying power for potential homeowners across the countrySix states – Louisiana, Arkansas, Iowa, West Virginia, Kentucky and Maryland – are seeing their lowest payment-to- income ratios in more than 25 years- While the fallout from COVID-19 continues to weigh on the broader economy, record-low mortgage rates and improved affordability appear to be providing a backstop for the mortgage and housing markets, with 19 of the 22 major markets analyzed seeing their median price per square foot rise from May to Junehttps://www.blackknightinc.com/black-knights-june-2020-mortgage-monitor/

@Devan Mcclish When you sub-meter you need to figure out who will actually be monitoring the meters.