Throughout the US, most buildings today are in range of a cellular telephone network and are already required to have smoke alarms. Today's smoke alarms could be replaced with all-hazard alarms. Building occupants could then receive alerts about floods, tornadoes, utility problems, public safety situations and all manner of other emergencies.

The all-hazard alarm would include a cell phone chip. The sending of alerts could be accomplished using the Cell Broadcast feature, which is far more efficent than making separate alert calls to each device. The basic service would be for incoming alerts only (distinct from smoke alarms that make outgoing calls to fire stations). 

Alerts would be sent sent over the cell network in CAP (Common Alerting Protocol) format. (The full CAP messssage, not just the SMS text "headline".) Cell equipment companies such as Ericsson could incorporate this CAP messaging feature into the cell network quite readily.

The cell processor in the alarm would have software to interpret alerts as to type of event, severity, certainty, and urgency. This would allow the building occupants to tailor the alarm for their particular needs. For instance, a nursing home would want a lower threshold for "urgency level" because more time is needed to evacuate such buildings. Others might choose higher thresholds to avoid "over-warning".

Further enhancements and customizations would be possible in such "smart, all-hazard alarms". Without much extra cost, such an alarm could emit voice narrative with warnings in multiple languages.

I am guessing the unit price of a "smart, all-hazard alarm" would be within a few dollars of a current smoke alarm. At that price, the market in the U.S. could exceed a billion units within a few years. And, of course, such alarms would be just as popular elsewhere in the world.