WASHINGTON, DC—As an additional reminder that the U.S. is on high alert for terrorist attacks, Secretary of Homeland Security Tom Ridge announced Tuesday that Orange Alert klaxons will blare 24 hours a day in all major cities.

Pedestrians in Manhattan maintain a high state of alertness thanks to an Orange Alert siren.

"These 130-decibel sirens, which, beginning Friday, will scream all day and night in the nation's 50 largest metro areas, will serve as a helpful reminder to citizens to stay on the lookout for suspicious activity and be ready for emergency action," Ridge said. "Please note, though, that this is merely a precautionary measure, so go about your lives as normal."

The sirens, Ridge said, will be strategically positioned throughout each city and will be audible within a three-mile radius. The noise will be loud enough to render conversation impossible within a 200-yard range.

"Some may find their normal sleep patterns disrupted, but it's a small price to pay to ensure our collective awareness of the heightened danger," Ridge said. "The key to preventing terrorist attacks is to have the threat constantly on your mind but still remain calm and act normal."

Ridge stressed that the government does not want individuals to let the blaring sirens affect their work or travel plans.

"Go about your usual business," Ridge said. "Of course, while you do so, keep in mind that we are just barely this side of Red Alert, the highest level of danger possible."

Ridge also urged citizens to pay close attention to the sirens' subtle variations.

"The steady 'alert' siren indicates the need to be generally aware of the threat of terrorism," he said. "This is the normal, default siren. The higher-pitched 'wail' siren, on the other hand, means federal authorities have credible information regarding a specific possible threat, and that citizens should ready themselves for the 30 to 50 percent likelihood of an attack. If citizens hear an 'alternating wail' siren, a piercing shriek/whine interrupted every 30 seconds by short bursts of what sounds like gunfire, they need to prepare for the 70 percent chance of a 20 percent more serious disaster. And, finally, a 'pulsating steady' alarm means Americans should have plenty of plastic sheeting and duct tape on hand to make a shelter in the almost guaranteed event of chemical, biological, or radiological attack."

A man urinating at D.C.'s Union Station is reminded to be extra vigilant.

Ridge emphasized that all these alarms merely indicate an Orange Alert state and not a 100 percent definite threat. Should the country be raised to Red Alert status, an entirely different set of patterned horn bursts would be put into use, the details of which will be available at www.fema.gov.

To make the alert system more responsive to subtle fluctuations in the national terror level, five new colors have been added between orange and red.

"The newly added levels are Orange-Red Alert, Red-Orange Alert, Maroon Alert, Burnt Sienna Alert, and Ochre Alert," Ridge said. "They indicate, in ascending order of fear: concern, deep dread, severe apprehension, near-crippling fright, and pants-shitting terror. Please make a note of this."

The sirens have already been introduced on a test basis in New York, San Francisco, and Atlanta. In spite of some complaints, most residents of the three cities are adjusting well to the warnings.

"The sirens are really loud," said San Francisco resident Linda Pearcy, shouting over a horn posted in her backyard. "My dog won't stop barking, and the windows rattle all day long. And I didn't know about the helicopters dropping all the orange slips of paper. I guess I can't complain, though. These are scary times, and the government is doing what it can to make us feel more secure."