Abstract: A test means for a smoke detector of light responsive type which includes a light source, a smoke chamber, a light responsive device sensitive to a light beam reflected from a preselected density of smoke in the smoke chamber for actuating an alarm signal, the test means including the same light source and light responsive device and having a separate test light path other than through said smoke chamber with light modifying means in the test light path to simulate a preselected smoke density. The test means includes a normally closed gate for said test light path, the gate being manually opened to transmit light along said test path to the light responsive device to cause actuation of the alarm in the absence of smoke in the smoke chamber.