This would include things like sensors and controls such as smart thermostats, lighting control, water meter flow sensors.

There are two thermostats, two air-conditioners, and two furnaces. 

I can get wholesale costs on smart lights locks and thermostats and have free access to a platform that allows for tenants to control their apartments through their smart phone as well as pay rent, request maintenance and communicate with me directly through their app.

And if walls are opened I insulate with foam.This property was occupied last summer, when it was frequently in the nineties, the thermostat was set at 72º - 24/7, and the highest electric bill was less than $100.

If you don't, you need to keep a lid on things i.e. water saving toilets, landlord thermostats, keeping a close eye if tenants are having several other people live there, car washing services on premises, etc.In the end, it all depends on how it cash flows and your tolerance.

You may want to look into technology as well like new smart devices such as thermostat, lights and so on.

The thermostats, for instance, you can manage from afar and most utility companies give you instant rebates on them. 

Estimating ~$40k to get electrical up to code & install new HVAC (currently one thermostat controlling all units).

Try to limit them as much as you can be limiting thermostats, water savers, motion detector lights and low wattage bulbs where reasonable.

Remote capability to set the thermostat or locksets is also good.