@Sherri14 @Debra300 @Jessica-and-Henry0 @Sarah977 @Anonymous
I'd suggest you send them an upbeat "just checking in/ how can we make your 30 day stay more enjoyable and close with. ".We'd ask that you please consider the environment and turn off lights, lower the thermostat, when not in use.."
To combat our $400/month electric bills, 2019, we added APP enabled features to our AC, Lights, Heat so we could "adjust". If you haven't already invested in NEST, etc products, now is the time! You could certainly attempt to engaging your guests in the solution--install NEST during your guests stay and have them be the "NEST test case", they might like the idea of being able to turn on the heat/lights 30 minutes before they arrive...
Whatever you decide to do, personally, when i need to address an issue with guests, I always take a moment to consider the guest perspective-how will they react to my message.
In this instance, some guests may be very uncomfortable with the realization that you are "watching them", it may not give them the warm/fuzzy feeling about continuing to stay with you. and check out.
net/net...I'd be very cautious what you write.