The Internet of Smart Things: using mobile phones as low-cost sensors

By: University of Oxford

Research at Oxford is demonstrating how cheap smartphones can be turned into low-cost sensors in a wide range of contexts.

Smartphones have reduced dramatically in price and can now cost as little as ten pounds. But they are effectively sophisticated computers with a range of high-tech features that make them highly adaptable as monitoring devices. Another great advantage is that they are immensely accessible: everyone knows how to use a smartphone app.

smartphones attached to electricity meters

Dr Russell Layberry of the Environmental Change Institute (ECI) has pioneered the use of smartphones for a range of applications such as monitoring energy usage, micro-climate, and the environment.

In comparison with expensive real-time monitoring systems, Android phones are mass manufactured, standardised platforms that offer a wealth of sensing and communication at a fraction of the cost. The microphone socket, for example, can be used as a sensitive volt-meter, allowing it to be wired up to an inexpensive data-logger (a programmable microchip connected to an array of basic sensors) and used to monitor anything that can be converted into a voltage.

Combined with the right low-cost ancillaries it can measure temperature, gas or electricity consumption. Even if no electrical signal is easily accessible, the phone’s accelerometer can tell whether a boiler pump is running, and image recognition software helps to ‘read’ meters and transmit the information.

A wide range of functions are possible. To measure moisture content in rock, for example, a voltage signal is passed via the phone’s headphone socket through the rock. Dry rock does not conduct electricity; wet rock, however, is a good conductor. The measured voltage therefore varies according to the degree of moisture, and gives a reading that indicates the moisture conditions of the rock.

And smart phones come with in-built communication. Once data has been collected it can be transferred using mobile or wi-fi networks. Their portability further helps in gathering data from as many locations as possible and building up a detailed picture over time without the need for multiple sensors.

The adapted smartphone is powered by the phone’s battery but can be configured to use only a tiny amount of power. Coupled with a small solar panel, it’s estimated that it could be self-sufficient for up to 2 years, or until the end of battery life. The phones can even monitor their own battery levels, turning themselves on and off to save power and deciding how often to send data – effectively making them able to run indefinitely.

The Dülük Baba Tepesi temple site in Turkey

The Dülük Baba Tepesi temple site in Turkey, where SmartStones are being used. Photo © Peter Juelich 2014

The applications for this technology are extremely varied. Katrin Wilhelm, part of the Oxford Rock Breakdown Lab in the School of Geography and the Environment is currently testing their use as remote environmental climate sensors on archaeological sites, monitoring fluctuations in temperature, humidity and light levels. The devices are called ‘Smart Stones’, since the plan is to disguise them as rocks to deter thieves and protect them from the elements.

Micro-climate measurements are made every five seconds and collected via an app on the phone. They are then streamed to the lab in Oxford via the 3G network, providing extremely detailed data that can be analysed at a distance and used to inform practical conservation measures. The monitor is vastly cheaper than other systems, which can run into thousands of pounds, and the data is more reliable and accurate than from local weather stations.

Katrin is also engaged in a pilot project with the former home to George Washington’s ancestors, Sulgrave Manor in Northamptonshire, monitoring the micro-climate inside the building as a key to preservation. Smartphone-based monitors could even be wired to switch dehumidifiers or heating systems on and off depending on the data readings, enabling indoor micro-climates to be controlled on a room by room basis, up till now, costly and prone to failure by other methods.

In additional, an art gallery is exploring the use of a light sensor attached to an adapted smartphone to automatically control the exposure of pictures and documents. Another potential use is in agriculture, where stored grain loses value if its moisture content is over a certain limit. Russ Layberry is also investigating the use of smartphones as air pollution monitors, the alternatives to which can cost city centres around £10,000 per year to install and run.

The next step is commercialisation. The research has attracted a NERC Pathfinder grant to investigate the commercial potential of the monitors, and it’s hoped that they will soon be out of the research lab and in to the streets, fields and buildings where they could make a world of difference.


This article originally appeared as the Oxford Impacts case study Smartphones become Smart Stones.  Find out more about the Oxford Impacts case studies series here.