Complete newbie here. I'm not using the right terms, so my apologies in advance.
The problem is simple. I want my powered computer speakers (2.1) to turn off when the computer is turned off. I have the same problem with my TV - it is connected to another set of powered (5.1) speakers. Right now I leave both speakers (computer/TV) always powered on, which wastes energy.
How can I create a "load sensing relay" which would monitor the power draw of the computer or the TV and if it goes above some threshold, to switch on the power line to the speakers? I'm sure that such thing already exists, but I don't know its name or how to find and buy it or to wire it myself.
I tried with a traditional relay, which was supposed to be driven from a computer/TV's USB port and when it is on, it would switch on the device connected to it. But this didn't work as both computer and TV's USB ports are always powered, even when the devices themselves are powered off.
That's why I want to monitor the power draw from the "input" device (computer/TV) and activate the relay if it goes above some threshhold (as the computer/TV draw some small amount of current even when turned off).