How to automatically lock a laptop screen using a Person Sensor.
The Person Sensor from Useful Sensors is a small, low-cost hardware module that detects nearby peoples’ faces, and returns information about how many there are, where they are relative to the device, and performs facial recognition. It is designed to be used as an input to a larger system, and this example shows how to use it to auto-lock your screen when you step away, and minimize the current window if somebody is looking over your shoulder.
To build this project you'll need a Trinkey RP2040 , a Person Sensor from Useful Sensors, and a Qwiic connector cable. No soldering is required.
Plug one end of the Qwiic cable into the Person Sensor, and the other into the Trinkey. They each only have a single port, and Qwiic connectors can only be attached one way, so it should hopefully be straightforward.
Hold down the bootsel button and plug the Trinkey into a USB port of your
desktop or laptop machine. You should see a drive called RPI-RP2 appear in
your file system.
There's a step by step guide to installing CircuitPython on a Trinkey
but the summary is that you download CircuitPython for the Trinkey,
and copy it onto the RPI-RP2 drive. Once the copying has completed, you should
see a new CIRCUITPYTHON drive appear instead.
The application works by emulating a keyboard and sending keypresses to the main machine to lock the screen, or minimize the main window. We need the adafruit_hid library to do the emulation, so the first step is to download a big bundle of all the CircuitPython libraries from circuitpython.org/libraries. You'll need to find the right bundle for your CircuitPython version.
Once you have that downloaded, unpack the bundle on your local machine. In the
file viewer, go to the lib folder within the unpacked bundle and copy the
adafruit_hid directory into the lib folder on the CIRCUITPYTHON drive.
This should install the library we need to emulate a keyboard.
If you're on Windows, the code in this repository should work with no changes.
On MacOS or Linux you'll need to modify what keys are sent to cause the screen
to lock. If you look at the end of code.py, you should see commented-out
options for the different operating systems.
Now your Trinkey is set up, copy the code.py file from this repository into
the CIRCUITPYTHON drive. You should notice that the green LED on the Person
Sensor lights up when it sees your face. If you point it away from yourself for
more than five seconds, you should find that the screen locks! It will also
attempt to minimize the current window if it detects somebody looking over your
shoulder for more than a second.
The sensor needs to be the right way up, with the connector at the top, and pointing towards you. If you have a long enough Qwiic cable, you can try mounting it on the top of your laptop screen.
The timings for the screen locking and window minimization are controlled by the
MAIN_FACE_TIMEOUT_SECONDS and LOOKIE_LOO_TIMEOUT_SECONDS values in the code.
You can also change how large the face needs to be to be counted with the
MAIN_FACE_MIN_WIDTH and MAIN_FACE_MIN_HEIGHT variables.
This project is intended as an example of what's possible when you can access ML capabilities as simply as any other hardware component. There's also an Arduino version available at github.com/robotastic/useful-autolock, and you can find out more about the Person Sensor from our full developer guide. We're looking forward to seeing what the creative minds of the maker community come up with, so please let us know how you get on!