A portable light or other device having a safety lock may comprise: a light body for receiving a source of electrical power; a light head including a light source for producing light and engaging the light body; and a lock mechanism engaging the light body or the light head and including a threaded member and a lock member. Rotating the threaded member moves the lock member radially relative to the light body and light head for engaging the lock for preventing removal of the light head from the light body unless the lock mechanism is released by a tool. A lock support may be disposed for supporting the lock member when the lock mechanism is engaged. The lock mechanism may be retained on the light body or the light head when the lock mechanism is engaged and when the lock mechanism is released.