Mains powered alarms are the most reliable domestic and commercial smoke alarms as they run off your home or buildings main power supply. Once the Smoke alarm is correctly installed you will not have to test the battery regularly, although they do have a battery back up in the event that you have a power cut. These smoke alarms need to be installed by a qualified electrician.
Linked or interconnecting alarms
If you have a large home or need a smoke alarm fitted in a commercial building then a linked or interconnecting alarm is recommended. These are smoke alarms that trigger other alarms to go off in the event of a fire. So when one alarm detects smoke all of the alarms in the property will go off alerting people all over the building that may not have heard the original alarm.