In the US, current fire codes require that hardwired smoke detectors also have a battery backup. http://artisanelectric.net/blog/the-big-picture/how-old-are-yo

In the US, current fire codes require that hardwired smoke detectors also have a battery backup. http://artisanelectric.net/blog/the-big-picture/how-old-are-your-smoke-detectors-when-was-the-last-time-you-tested-them/ http://artisanelectric.net/blog/the-big-picture/how-old-are-... http://www.nfpa.org/codes-and-standards/document-information-pages?mode=code&code=72 http://www.nfpa.org/codes-and-standards/document-information...