The present study reports 832 telephone interviews during the spring of 1984 with persons from two insurance companies in the same geographical area. In the fall of 1982 one of the insurance companies started to distribute a free smoke detector to all of its customers. The other insurance company served as a control and comparison group for studying the effects of a free smoke detector on installation and reliability. The population in each insurance company was stratifed into two insurance policy groups, and crossed with three age groups. Random samples of approx equal sizes were drawn. Around 94 percent of the persons in the samples were actually reached, and the interview about installation and reliability ended with a request to press the test button of the smoke detector. The net effect of sending out a free smoke detector is more pronounced with household policy holders, although home policy holders more often have a smoke detector installed. There is no general tendency that people who have bought a smoke detector take better care of it, maintain it better, install it in the right place more often, check it more often, or make it operate properly more often than those who have got a free smoke detector. However, for old people the free smoke detector has been out of working order more often than for young people. Any such effect of a free smoke detector is not more pronounced with those who have a household insurance policy than with those who have a home insurance policy. Nor is there any such effect of age group. It should be noted that around 16 percent of the smoke detectors that are reported by their owners to be in working condition, do not respond to the test-button being pressed.