This photo of the weapons briefcase was spotted yesterday on the wall of a Manhattan police station house.

On the outside, the briefcase looks like what any Wall Streeter would lug to work. But on the inside, instead of a businessman's papers and folders, there are numerous vials of deadly chemicals wired to a cell-phone device and apparent detonators.

Officers have been ordered to watch for terrorists trying to pull off an attack in the city by stashing deadly chemicals and explosives in common household items and then trying to smuggle them into crowded subway stations or sporting events.

They have been told that deadly poisons such as cyanide and the nerve gas sarin may be hidden in items including briefcases, light bulbs, soda bottles, aerosol cans, fire extinguishers and even mayonnaise jars.

The warnings - from the NYPD's counterterrorism unit - came as Homeland Security czar Tom Ridge called the latest alert "the most significant warning since 9/11."

Authorities have said they expect that if an attack occurs, it will come after Valentine's Day.

They urged Americans to be ready by stockpiling a three-day supply of food at home and buying material to seal their homes in case of a chemical or biological attack.