Windows/Mac: Your computer's webcam can be useful for more than just quick photos and video calls. The Webcam Pulse Detector is a fun, open-source application originally designed at NASA to use your connected camera to take your heart rate. Now you can try it out at home.
The utility is simple to use. Just grab the executable and run it. It's a self-contained python application, so it shouldn't need any dependencies or other files to work. Once you open it, you'll get a view of your camera, and it will ask you to guide your face into view so it can get a fix on your face and your forehead. Once it's in the right position, press S to lock your face, and watch the app take its readings. You'll even get a little graph (if you press D) that shows your heart rate over the time you've had the app open.
To be fair, it's not perfect at all. My readings tended to be particularly low (maybe it has more difficulty with people of darker complexion) but it seemed to work pretty well for others. The Webcam Pulse Detector is available for Mac and Windows in pre-compiled binaries, and a version for Linux is on the way soon. You can check out the project homepage (and download it to try yourself) below.
Webcam Pulse Detector [GitHub]