For example, I use programmable deadbolts for entry.

One for each floor and each floor has its own thermostat.

I've been listening to the BiggerPockets podcast for a few months now, am in the process of reading Brandon's book on REI, and am just trying to immerse myself in all things real-estate.I work as a programmer in the financial industry, so currently I'm most familiar/comfortable in the stock market with mutual funds.

One is on the kitchen counter, one resting on the thermostat, one on the coffee table, and one on the end table by the sofa.

A way to remotely control the thermostat or take away their access.

The bane of all landlords.I highly, HIGHLY recommend you take the thermostats out of the individual apartments.

I'm a computer programmer recently introduced to "Rich Dad, Poor Dad" by my wife. 

Nest thermostat to keep temperature within acceptable range.5.

. - Install two new high efficiency condensing boilers, and update windows and insulation for better heat loss performance.PROS - a) minimally invasive; b) can provide 15-30% reduction in heating costs (we are told).CONS - a)total gas expense is still paid by the landlord; b) individual units won't have individual control (except for a thermostat controlled shutoff valve for heat/water in each unit); c) AC would be available on with in wall/window units. 2) Try to individually meter each units' gas and provide each with a traditional forced air heating/cooling system.PROS: a)gas expense could be completely removed for landlord (huge)- even tankless hot water could be installed in each unit; b) each unit would have their own climate control.CONS: a) constructions costs of running new gas lines and soffiting sheet metal duct work. b) highly invasive with collateral construction costs; c) future costs of maintenance on multiple systems vs a single building-wide system. 3) An electric based heating system- This is tricky in my mind because of the high cost of electric heat.

Her boss has been real cool to her and allows her to do half of her work at home.She is a computer programmer and has been saving in a 401K for about 25 years so I am not under tremendous stress.