For Your Information.
In Australia. My wife and I own two rental properties, and our estate agent has recommended a specialized smoke alarm maintenance company. The idea is that if the house burns, and the police can prove that the smoke alarm was defective, or had a flat battery, the owner could be liable for negligence. Our agent gave us the choice: sign up, or declare that we will look after our alarms ourselves. We live 450 km from our properties, (was not planned that way) so we signed up for the service. $99 a year, and the smoke alarm company will visit 2 or 3 times a year, replace batteries if needed, replace the alarm if needed, and change the location of the smoke alarms if needed.