Sense a load - Save Energy on Inverters and USB-Chargers

[merkatorix]

Short Background
When using a battery to power an inverter or USB-Charger, the idle current annoys me a bit. I really would like to see it to be negligible compared to the self-discharge of Li-ion or at least Lifepo4 (Offtopic: I'm a battery beginner and wonder if my future Daly BMS will compete in this department).
The easy solution: Switches for every consumer. However, I'm lazy and like stuff to be simple for the user (and I search for reasons for automation.)
Question
Is there a way to sense if some load is plugged into the inverter or USB charger? If possible, I could use a µController, which senses the load and only turns on the devices if an actual load is connected.

There might be a mechanical solution if it is only about the plug. But there could be a plug in the socket without any load attached. I imagine there are two levels within this question:

• Sense the load before turning it on.
• Sense the load while a device is running.

I wonder if there are feasible ways to sense a load. I could imagine a method for both cases, but I wonder if there are much better ways to tackle the problem.
Just after turning on the battery, I could imagine it to be possible to sense if something is plugged into the plug by applying a small voltage and checking if some current flows. If there is a µController present, there is 5V, which could be connected to USB sockets. If the load starts to draw current, it could be connected to the actual USB-C charger.
I imagine the same to be possible for 230V devices; however, there will be a whole topic about electric safety. If that could work out, an appliance could be sensed without any chargers or inverters having to be in an idle state.
 
If a device is already plugged in and the inverters/chargers are running, I imagine the problem to be more challenging (Especially for the 230V of the inverter). In that case, a shunt could be used. For 230V, maybe an intelligent power plug, which already has an integrated shunt?
If there is less than X mA peak power consumption for an hour or something, we could turn off the device and start to sense if an actual load is present.

I bet there are established methods for this problem used by people, who usually don't use trash bags as a weather-resistant case for their products. Do you have hints? In the end, just using shunts everywhere might be feasible and not too much effort for a small project, which should end up in a big universal power bank using cheap Lifepo4 cells.