A Hand Wash Sensor built from Off-the-Shelf Hardware

To help the 20 second hand wash, we built a version of our hand wash sensor with off-the-shelf hardware

Adam Dunkels, Thingsquare CEOBy Adam Dunkels, Thingsquare CEO – March 25, 2020, Updated March 26, 2020

Updated to add link to instructions on how to build one yourself

To help reduce the spread of the COVID-19 Corona virus (and most other types of viruses and bacteria), we designed a hand wash sensor to help us wash our hands for those 20 seconds.

See it in action here:

The sensor detects that someone is standing in front of the sink. Then starts to blink:

  • A red blink for 20 seconds to indicate that we should keep washing
  • A quick green blink to indicate that we are done

The idea is that this will help us keep the 20 second habit up.

The sensor also measures how long we wash our hands and reports this data

We previously built a version of the sensor with a custom piece of hardware, including a passive IR (PIR) sensor.

We now have designed a version of the sensor that uses only off-the-shelf hardware: the LPSTK.

The LPSTK has a built-in light sensor that we use for detection: if is gets slightly darker, we take this to mean that someone is in front of the sink. Likewise, if it gets slightly lighter again, we take this as an indication that the person went away again.

We use the wireless all-IP mesh network created by the LPSTKs both to report the hand wash statistics and to configure the hand wash sensor.

The stats

To make it more fun to actually hit that 20 second mark, the stats from each hand wash sensor are collected and displayed on a screen.

The data is also stored in the database so that we can compare different locations with each other. Which bathroom has the best hand wash stats? With the sensor, you will be able to find that out!

How to set it up

Installation is simple: just place the sensor behind the sink, so that the light sensor faces the sink. To make the sensor stick to the wall, a piece of double sided tape made for tiles can be used.

To access the stats from the sensors, an access point is needed, which can be built from a LPSTK and a Raspberry Pi.

Instructions for how to build this yourself are available here.

If you are interested in trying out the hand wash sensor in your office or place of business, you can also get in touch with us and we’ll be happy to help you set it up.

Download firmware files

The firmware files for the hand wash sensor can be downloaded here:

Note that these are provided for evaluation purposes only and may not be used commercially (see full terms of service here).

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Adam Dunkels

Adam Dunkels


Fredrik Rosendal

Fredrik Rosendal


Marcus Linderoth

Marcus Linderoth

VP Engineering

Setting things up...