Smart nappy with ultra-cheap sensor tells you when it’s wet

17 Feb 2020

Image: © AUFORT Jérome/

Engineers have found a rather simple way to make a ‘smart nappy’ that can tell when it’s time for a change.

In the latest attempt to make parents’ and carers’ lives that little bit easier, researchers from MIT have developed a ‘smart nappy’. Made from existing nappy material, this new device is embedded with a moisture sensor that alerts a parent or caregiver via a smartphone when the baby needs changing.

The sensor consists of a passive RFID tag placed below a layer of absorbent hydrogel. When it gets wet, the material expands and becomes conductive enough to trigger the RFID tag and send a radio signal to an internet-connected device up to one metre away.

The researchers said this is the first demonstration of hydrogel being used as a functional antenna, and with the sensor costing less than 2c to manufacture, the nappy would be a low-cost, disposable device.

Over time, they added, it could be developed further so that it could record and identify potential health problems, such as signs of constipation or incontinence. The sensor could also be used among nurses in neonatal units for monitoring multiple babies at a time.

Not just for babies

Researcher Pankhuri Sen said that the smart nappy would also be useful among adults.

“Diapers are used not just for babies, but for ageing populations or patients who are bedridden and unable to take care of themselves,” Sen said.

“It would be convenient in these cases for a caregiver to be notified that a patient, particularly in a multi-bed hospital, needs changing. This could prevent rashes and some infections like urinary tract infections, in both ageing and infant populations.”

Publishing their findings to IEEE Sensors, the researchers said the smart nappy’s sensor resembles a bow tie, with the RFID tag connecting the bow tie’s two triangles. Each triangle is made from the hydrogel super absorbent polymer, or SAP.

They also found that adding a small amount of copper to the sensor could boost its conductivity as well as the range that the tag can transmit a signal.

Colm Gorey was a senior journalist with Silicon Republic