Check all the keys of a keyboard
Javascript, 524 bytes
Hi, this is my first ever post here, so excuse me if I'm still ignorant on some stuff, I think I stayed within the rules though.
k=[8,9,&quot;130&quot;,&quot;133&quot;,&quot;161&quot;,&quot;162&quot;,&quot;171&quot;,&quot;172&quot;,&quot;181&quot;,&quot;182&quot;,19,20,27,44,45,46,48,49,50,51,52,53,54,55,56,57,144,145,186,187,188,189,190,191,192,219,220,221,222];for(i=32;i&lt;124;i+=1){i&lt;41?k.push(i):i&gt;64?i&lt;91?k.push(i):i&gt;95?i!=108?k.push(i):0:0:0}d=[13,16,17,18];m=document.addEventListener;c=console.log;m(&quot;keydown&quot;,e=&gt;{e.preventDefault()});m(&quot;keyup&quot;,e=&gt;{c(e.code);if(d.includes(e.which)){l=e.which+&quot;&quot;+e.location;if(k.includes(l)){k.splice(k.indexOf(l),1)}}else if(k.includes(e.which)){k.splice(k.indexOf(e.which),1)}c(k.length)})

It seems buggy if I don't use Chrome, but you can try it out here.
(be sure to open the console before you focus on the example window, as the default functionality of F12 is prevented)
Overview
The program makes an array of all the 101 &quot;keycodes&quot;. Some are written explicitly, some sequences are added with a for loop and some are stored as strings. I have a seperate array for the &quot;double&quot; keycodes, since left and right control for instance give the same keycode. They also give a location, however, so I combine the keycodes with the locations as strings in the array. From there it's just an eventlistener that prevents default keydown functionality (don't wanna refresh with F5 in this case) and a seperate eventlistener for keyup, because every single key can be detected on keydown, EXCEPT FOR PRINTSCREEN.
After every keyup event the remaining keys (aka the length of the array) gets logged, as well as the name of the keycode (so there is the distinction between left and right shift, etc). I wasn't sure if that was a requirement, if not you can subtract another 10 bytes from the score.
Limitations

It only seems to work well in Chrome

I hope this answer is appreciated and please let me know if I've done anything wrong.