How does a stackmat timer work?

[Tigerninja]

I've tried pressing it with cubes but that doesn't work, so I believe it's sensing the hands' warmth. Does anyone know anything about this?

 

[Curunír]

I've tried pressing it with cubes but that doesn't work, so I believe it's sensing the hands' warmth. Does anyone know anything about this?

It depends on the brand like YJs pocket timer uses infrared but I believe my one a regular YJ timer detects my electromagnetic field.
I am not sure how a G5 works though