Technology probes is a new type of probe that combine the social science goal of collecting information about the use and the users of the technology in a real-world setting, the engineering goal of field-testing the technology, and the design goal of inspiring users and designers to think of new kinds of technology to support their needs and desires. Washing hand detector is a project to investigate and learn the data-driven design research method, technology probe through practice.  A washing hand detector was designed and installed in a public toilet, to study the probability of people washing their hands.


Washing hands properly removes dirt, viruses and bacteria to stop them spreading to other people and objects, which can spread illnesses such as food poisoning, flu or diarrhoea.

“Hands are easily contaminated with faecal bacteria [poo] when going to the toilet and this can be easily spread on to other things you touch, including food. Unfortunately, not all people consistently wash their hands after going to the toilet or before handling food.”
- Professor Jeremy Hawker, a consultant epidemiologist at Public Health England.

Washing your hands properly should take about as long as singing "Happy Birthday" twice (around 20 seconds).

Washing hands instruction by NHS


- To study whether people in the Evolution House wash their hands after using the toilet.
- To investigate how long they wash their hands for.
- To evaluate the effects of individual practices on the cleanliness of the environment.


Because it is:
- confidential, as the question cannot be researched by using observation.
- appropriate, as it records data from simple uses.
- efficient, as the data needs to be tracked at all times.


In order to collect data on people washing their hands, I tried to detect if the tap was open. Three different kinds of sensors were tested: the ultrasonic sensor, to detect the distance between water and the sensor; the accelerometer, to detect the vibration of the tap; and the noise sensor, to detect the noise of the water. However, none of these sensors worked properly. To find out if people entered the toilet, I tried to use a digital compass on the door, to detect whether the door was open.

Testing different sensor and data collected


Finally, a door switch sensor was attached to the toilet flush handle, to detect if people used the toilet (upper right image). Conducting wires  connected water from the tap to the analog pin of the Arduino (microcontroller), to read the currency in the circuit in order to detect if the tap was open (lower right image) .

The final circuit


To deploy the probe in the toilet, several constituent parts are designed. A bracket was designed to fix the conduct wires on the tap and a clip was designed to fix the door switch sensor on the flush handle. Shells are designed to contain the Arduinos and the power banks. All designed constituent parts are 3d printed. A customised shield integrated all electrical components is built to stack on the Arduino. The probe was pre-tested before the final deployment.

Design and making processes


Video of deloying technology probe


The two Arduinos recorded at what time the people washed their hands and used the toilets. The Arduino switched on within seconds in the CSV file (image below). The data was analysed and transferred  to real time by Python—a programming language. Plots were created (left image), showing the time people spent washing their hands and using the toilet. The plots show that there are different reasons for the extreme data.

Data in CSV file


As the plots on the left, the extreme and hard-explained data are cleaned. Based on the data, users’ behaviours in the toilet are estimated and indicated on the plots.



In the washroom, where the technology probe was installed, 72% (31 out of 43) of people washed their hands after flushing the toilet.

The average time people spent washing their hands in the washroom was 6.85s, which is much less than the 20s suggested by the NHS. People on the first floor of the Evolution House may need to promote hand-washing awareness.


In this project, the technology probe showed low accuracy results.  Some data captured was difficult to explain.

The assumptions were difficult to confirm, as requesting information on people’s toilet habits is not appropriate.

The technology probe as a design research method needs to be combined with some other human-centred methods to be more effective in certain situations.

If the technology probe could be installed in the toilets on other floors, the data would be more representative.

The lights on the box may be a distraction to those using the toilet, even if they are only meant to show that the sensors are working properly.

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