Replace batteries, check cables or buy a new device if necessary.7.

Just set it up on the window sill with windows opened and turn it on--they sell battery operated ones for convenience and the charge lasts pretty long since its used strictly for ridding moist air when bathing. 

I also have a lockbox that I would give guest access to in case the battery goes out in the smartlock or if they find a creative way to lock themselves out of the house with the deadbolt locked.

If I don't hear from them by the next day or so, I send them a text asking them to check their email; I then usually get a reply email within a couple of hours after I send the text.When I go to the house, I have everything I know I'm going to need (filters, batteries, etc). 

@Jason James Tesla is opening the largest battery factory in the world (called the GigaFactory) just outside of Reno in 2 years and the general business climate is improving.  

I would go with a battery operated (stand alone), which is the cheapest route to go. 

I'm talking about gas, oil, tires, battery, wiper fluid, etc. etc.

Misuse of the batteries could cause damage, but the same could be said for most other modern portable electronics.

Authorities always encourage everyone to change the smoke detector batteries at the beginning of the new year. 

For example, I scheduled a vendor to install the new 10 year lithium battery smoke and carbon monoxide detectors.