Because events such as natural disasters or bombings often knock out phone and Internet networks, trapped people cannot make normal calls, send texts or email for help, the said.
"They are in an island of non-connectivity," said Amro Al-Akkad, an engineer with the Fraunhofer Institute for Applied Information Technology .
A colleague, Leonardo Ramirez, realized an app could be created that could insert a short SOS message into the name field of a phone's WiFi hotspot, which broadcasts a radio signal without requiring Internet access.
Rescuers would be able to read the message with their own WiFi app.
The two apps, a "victim app" and a "seeker app," would connect rescuers with trapped people, the researchers said.
With the victim app a trapped person could write a 27-character message -- possibly something like "injured, trapped in basement" or "fire on 2nd floor, elevator stopped" and the seeker app could pick up the message from up to 100 yards away, they said.
The team consulted emergency workers from the Haiti and Fukushima, Japan, earthquake disasters to find out the best way to write the apps.
"They wanted it simple, unencrypted and smart," Al-Akkad told NewScientist. The researchers chose to avoid low-power, low-range Bluetooth radio links which often fail to connect -- or "pair" -- with each other amid the clutter of metallic debris in broken buildings, choosing much more robust and receivable WiFi radio instead.