Babies have a pretty effective method of letting their parents know it's time for a diaper change.

It's called crying.

But researchers in Japan think they've hit upon an even better idea: a cheap, disposable sensor that uses wifi to signal when a diaper is wet.

"If sensing is done electronically, you can tell simply by coming close to the wearer--without unclothing him or her," one of the researchers behind the new technology, Tokyo University electrical engineering professor Dr. Takao Someya, said in a written statement. The alert might come in the form of an audible tone on a smartphone, he said.

And wireless nappies are just one possible application of the prototype diaper's underlying technology--described by its developers as the world's first wireless organic sensor system that's flexible. Other possible applications include bandagelike medical devices to monitor a patient's vital signs.

"Mechanical flexibility of electronic devices is very important to open new applications in medical and healthcare use although the current devices are all made of hard materials," Someya told The Huffington Post in an email. "In the future, the new wireless flexible sensor will be used as a... sensing system that measures various kinds of vital information for medical and healthcare use without causing any discomfort of wearing when applied on human skin."

Another possible use of the technology is in industrial sensors capable of monitoring the temperature of food to guard against spoilage, Someya said. He added that the flexible integrated circuit at the heart of the technology can be fabricated at low cost with simple ink-jet technology.