Wireless sensors can tell your smartphone when food in your fridge is about to go off

Researchers have developed a low-cost wireless sensor that could tell you when food is starting to spoil before you could - even sending an alert to your mobile phone.

The chemical sensors look a bit like a those anti-theft stickers that shops sometimes attach to products - but instead of setting off an alarm, these ones detect gas.

The amazing thing about the sensors is they require absolutely no power.

They just sit there - in your fridge or in a factory - and can then transmit data when they are placed near a reader - which could be your mobile phone.

The technology behind these sensors is near-field communication (NFC) - similar to that used in contactless credit cards and some smartphones.

These NFC sensor tags receive the little power they need from the device that reads them.

The research team - from MIT - took existing NFC tags and modified them, punching a hole in them to break the electrical circuit and then using a very special pencil to re-complete the circuit.

That pencil is made from carbon nanotubes which are designed to detect a particular gas - ammonia or hydrogen peroxide are some of the gases they can identify.

When the nanotubes bind with a particular gas, their ability to conduct electricity changes, and this change can be detected by the reader device.

The researchers developed the sensors to be read by smartphones - but at the moment the sensors can only detect one gas at a time and the phone needs to come within 5cm of the sensor to read the data.

The team is working on Bluetooth technology that would expand the range.

Eventually we might reach a point where the sensors could sit permanently in your fridge and send an alert to your smartphone telling you your chicken’s about to go off or your cheese is a bit funkier than it should be.

The idea is to try and avoid food waste - we throw away 7 million tonnes of food from homes in the UK alone each year.

It can also be used to detect explosives and even signs of disease in people's breath.