The SW1 is a mains powered heat alarm with 9V battery back-up and improved Push-Fit base for quicker and easier installations; designed to ensure quick and easy installation of base unit to the mains feed supply at installation stage (1st fix) and for quicker and easier connection of alarm to base unit (2nd fix). The HW1 provides class A2 heat detection 54C ? 70C, suitable for use in areas not generally recommended for traditional smoke alarms such as kitchens, attics and garage spaces.