A civil defense siren is a mechanical

Machine

A machine manages power to accomplish a task, examples include, a mechanical system, a computing system, an electronic system, and a molecular machine. In common usage, the meaning is that of a device having parts that perform or assist in performing any type of work...

 or electronic device (modern-day sirens are electrically powered

Electric power

Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...

 whether they are electronic or mechanical) for generating sound

Sound

Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...

 to provide warning of approaching danger and sometimes to indicate when the danger has passed. In some areas in the United States, civil defense sirens may sound in the late morning and early afternoon on a regular basis. In places like Haxtun, Colorado

Haxtun, Colorado

Haxtun is a Statutory Town in Phillips County, Colorado, United States. The population was 982 at the 2000 census.-Geography:Haxtun is located at ....

 the siren goes off at 7 a.m., noon, 1 p.m., and 6 p.m.