Today we are going to talk about smoke and carbon monoxide detectors in your rental property. You must understand that the laws have changed for smoke and carbon monoxide detectors.
Before 2014 a lot of landlords would put in their leases that the tenants were responsible for the maintenance and making sure that the smoke detectors worked but the laws have changed a lot since 2014 . Now it really puts a lot of responsibility back on the owner. The first law was July 1st of 2014, the law said all smoke alarms including combination smoke alarms and carbon monoxide, that are solely battery powered shall contain a non replaceable, non-removable battery that is capable of powering the smoke alarm for at least 10 years. This means using 10-year lithium batteries to be compliant. The law also said that people could finish their stock up at the time but at this point, we are in 2020 and your stock is done.
If you are installing a smoke detector it needs to be a 10-year lithium battery, especially in a rental property. On January 1, 2015, they made some las that were for the manufacturers. In addition to the 10-year sealed battery requirements, the bill also requires smoke alarms and combination smoke and carbon monoxide alarms to display the manufacture date, provide a place to write the date of installation on the device. This means that it is your responsibility to write the installation date and the expiration date
About 70% of the properties that we take over do not have the smoke detector date of installation written on them. This is putting you not up to code. The law also requires that by January 1, 2016, owners of a dwelling unit intended for human occupancy in which one or more units is rented or leased shall install an additional smoke alarm, as needed, to ensure that smoke alarms are located in compliance with current building standards and incorporate a hush feature. (A “hush” feature will momentarily silence the alarm to allow whatever set off the alarm, such as smoke from the kitchen, a chance to dissipate. A “hush” feature, however, does not turn off the smoke alarm, and after a few minutes, the alarm will return if the smoky conditions persist.) 
Presently the California State Building Code requires that smoke alarms be located in 1) the hallway outside the bedrooms 2) in each bedroom and 3) on every floor regardless of whether there is a bedroom on that floor. … For all other homes, the smoke alarm may be battery operated. (Cal. Health & Safety Code § 13113.7.) Carbon monoxide detectors do not need to be in bedrooms just one per floor. So if it is a 3 story house you need to have 3 carbon monoxide detectors.