On: What's that touchscreen in my room?

[teekert]

P1 port is specifically to read values and “open”. There a 10€ cable to convert it (passively) to usb.

You could consider one of those clamps that measure the power through a cable from the fields around it?

[dancsi → teekert]

Actually, it is just serial under the hood, although electrically slightly nonstandard.