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The U.S. Sloop of War <em>Alert</em>.

Alert

The U.S. Sloop of War Alert.

A device on an automobile for making a warning noise.

Automobile Horn

A device on an automobile for making a warning noise.

The door knocker is used to alert people inside the home to open the door by making a knocking noise.

Door Knocker

The door knocker is used to alert people inside the home to open the door by making a knocking noise.

The door knocker is used to alert people inside the home to open the door by making a knocking noise.

Door Knocker

The door knocker is used to alert people inside the home to open the door by making a knocking noise.

Incandescent bulbs are made in a wide range of sizes and voltages, from 1.5 volts to about 300 volts. They require no external regulating equipment and have a low manufacturing cost, and work well on either alternating current or direct current.

Incandescent Lamp

Incandescent bulbs are made in a wide range of sizes and voltages, from 1.5 volts to about 300 volts.…

A siren is a loud noise maker. The original version would yield sounds under water, suggesting a link with the sirens of Greek mythology. Most modern ones are civil defense or "air raid" sirens, tornado sirens, or the sirens on emergency service vehicles such as ambulances, police cars and fire trucks. There are two general types, pneumatic and electronic.

Noise Making Siren

A siren is a loud noise maker. The original version would yield sounds under water, suggesting a link…