Non intrusive controlling & monitoring system
On/off control is, by definition, intrusive. ie
 The act of turning something off IS intrusive.
 The act of turning something on IS intrusive.  

BUT:  

You can measure AC current without intrusion and
 You can measure AC voltage with very close to zero intrusion.   

While it IS possible to monitor voltage without intrusion in the strict sense
 ie with no ohmic connection, by using eg capacitive coupling,
 there are few circumstances where this makes practical sense.
 Even DC voltage may be measured using electrostatic methods but this would essentially never be done in AC mains measurements.
 Long long ago I did see and electrostatic DC  meter ! Rare.

Ac current can be measured by detecting the field produced - most usually with a Hall sensor.
 Special ICs are made for this purpose.

Clamp meters of the sort shown by Rocketmagnet in his answer are also useful. 

Here is an AC current sensor which uses a Hall sensor.
 The current path is built into the IC for precision but this is not essential.
  There is no "ohmic" contact with the current path.