This is cheap with battery-powered materials, if your local code allows it, significantly more expensive with hard-wired models if your local code doesn't allow them.

Replace all old detectors or at least put a fresh battery in.

I replace old smoke detectors with the 10 year lithium battery ones that are built in. 

My electronic lock is on a 9V battery.

However, with the normal wear and tear/ usage of the two main entry doors to the units foyer area, we have had more than 5 service calls on the locks (for batteries, lock mechanism not functioning, etc.) and both front door Locks have had to be replaced once already and I am thinking it is time to use a different Door Lock method. 

The Kidde Access Point is the best. https://www.amazon.com/Kidde-AccessPoint-001414-Co...Electronic locks are great, but you'll always want a spare in case the battery dies.

Great job 809 credit score. 12 hits on criminal record the worst being battery with intent to cause physical harm (3 counts total) and Burglary of a Dwelling.

The small town rumor is that dude is the dope man and he has a laundry list of small-time drug and some more significant battery convictions already.

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In 2020, new homes in California will require them. http://www.jlconline.com/business/california-mandates-solar-panels-with-a-battery-option_o