Today's alert has been triggered by "high" levels of air pollution.
Today's alert order is likely to be just the first of many in the weeks to come, officials said.
Like the intelligence that led to the earlier threat advisory, the information behind today's alert stood out from the stream of threats and warnings received by law enforcement and intelligence agencies each day, the officials said.
And today's "alerting" tools are quickly being crushed by services, like IFTTT, that build workflows into our lives.
Although today's alert was sent by FEMA, any future presidential alert can be sent solely at the discretion of the president and can be issued for any reason.
Most, though not all, of the information that triggered this week's alerts concerned the early surveillance stage dating back several years, rather than later operational activities.
Ahead of this week's alert, Beijing had already been in a state of orange alert, meaning some construction and industry had been curbed.
Today's loss alerts are a variation on the stop-loss orders that brokerages have offered for years.
Users signing up to USA Today's text alerts for news, sports, gossip, etc. will receive real-time updates and a sponsored interactive ad.
Responding to this week's heightened alerts, Howard Dean mused "it's just impossible to know how much of this is real and how much of this is politics, and I suspect there's some of both in it".Large numbers of Mr Bush's opponents are convinced Osama bin Laden is locked up and waiting to be revealed in handcuffs in an "October surprise".
A hearing with Hawaii lawmakers on Friday revealed that Gov. David Ige knew last weekend's missile alert was a false alarm two minutes after it was broadcast across the state, but didn't notify the public of it until 15 minutes later.
