A hardwired smoke alarm is connected to the main power supply of a property and powered by 240V but will also have a back up battery, adding extra protection in the case of a power failure or blackout. There are two different types of hardwired smoke alarms: ionization alarms, which are the most common. Ionization alarms are prone to trigger with high heat and small amounts of smoke because of their technology to effectively sense smaller, fast burning fires. Photoelectric alarms use light sensor technology to detect smoke particles with the reflection of mirrors and light inside the alarm chamber. These smoke alarms contain no radioactive materials either, making them safer to dispose of. The difference between both alarms, is an ionization alarm will respond to fast burning fires and a fire with a larger flame. Photoelectric alarms will respond better to slower burning and smoldering fires. You will require an electrician install and replace hardwired alarms. Then there is an option of 9V battery alarm. These are the cheapest option when it comes to smoke alarms. They can be easily installed and only require a 9V alkaline battery to operate. They still have a ten year life span, but it is important to remember the batteries in these alarms need to be changed every 12 months.