"Interconnected smoke alarms can be an important part of family home safety. However, many older homes do not have the wiring installed for interconnected smoke alarms. Wireless smoke alarms listed by Underwriters Laboratories are now available. The safety of interconnected smoke alarms can now be installed without the expense, messy wiring or cost of a licensed electrician. Both battery powered and AC powered alarms are available to fit almost any residential structure. Wireless interconnected smoke alarms are easy to install and only involve a few simple steps. The first step is to determine what type of smoke alarms are currently in the home: battery powered, hardwired or hardwired with interconnect."
Coffee Break Training - Fire Prevention and Public Education Series No. FM-2013-10
United States Fire Administration: http://www.usfa.fema.gov/