Smart thermostats?

for example, if we send someone out for a heater repair, but it was due to a battery in the thermostat... we charge the tenant. 

We do not use the programmable ones as they are higher maintenance, and much more “busywork” setting the code each time which becomes cumbersome at higher volume.. and if you forget to Chang the code to their phone number it sucks for the guest.  

The plan is to put in a Nest, or similar, thermostat in the whole way (under a lock and key) so to be able to control the temperature from wherever. 

If the temp was too high, they'd open a window, of course playing games to get the thermostat cranked up. 

My tenants decided they wanted to updgrade the thermostat so they could control it remotely and tried to replace it without ever notifying me - until they damaged the wires so badly that now an electrician needs to fix it.

One of my housekeepers is fairly tech savvy and can do those things (I'd be okay with him doing a Roku install, but for stuff like my smart thermostats and Ring cameras I DIY).  

I work as a SAP programmer but honestly I am sick of working for someone else and making someone else rich.

I realize they are easily removable but at this point i am familiar with how each apartment responds to the different temperature settings of the thermostat as i have made temperature observations during periods of vacancies so I would know if a window is open etc.  

Today I raked leaves at my flip that is for sale, worked in marketing of a vacant unit, wrote a list of things that need doing in order to clear my furnished rental, to make it ready to rent empty - scheduled Occupation Inspection with the city; changed batteries in the thermostat so that my tenant has heat.