Smart Building Monitoring - Sensor Selection

Hi all, I am to designed a smart building monitoring system in the campus using Arduino and ZigBee. I am required to monitor the energy consumption of the computer and projector in the lecture room without disturbing/invading the original system. What sensor should i be using to just detect if the computer/projector is on/standby/off? Appreciate you help on this. Thank you

Appreciate you help on this

Appreciate you not cross-posting.

Duplicate deleted.

You say:
I am required to monitor the energy consumption of the computer and projector in the lecture room without disturbing/invading the original system.

I say:
Buy a watt meter for 15 bucks and done