One of the simples methods of sensing loads is to use a low-Ω resistor (0.1Ω or less) in series with a load and connect 5/230V transformer with the 5V winding in parallel with this resistor. By doing this you have gain of ≈44, and now this signal can be used by an ordinary comparator to acitvate something (relay, LED, ..) ..
Also, this circuit provides isolation from dangerous mains voltage ..
Regards,
IanP
Attached is your circuit ..
As +12V supply for this circuit you can build a power supply with 7812 voltage regulator in its basic configuration (see attached picture) with 230/12-15Vac transformer ..
Regards,
IanP