In commercial premises and in private households, the installation of smoke detectors can save lives. Most are fitted with a test button to test their correct operation. However that fails to detect whether faults in the device are preventing smoke from reaching the sensor. Smoke detector test sprays close this safety loophole. By generating a fog, the test spray simulates the presence of smoke. The spray is colourless and odourless, it leaves no residues on walls, ceilings or on the device itself.