Cheap Current Sensing/Feedback

Hello, I have many automated devices in my home via arduino/processing/web/blah blah blah but my biggest issue is not knowing (via arduino) if the actual device is on or not. I have created a board with a couple ACS712s on it to sense current but it's somewhat of an expensive process. So my question is, is there an easier way to receive feedback from the lamps/tvs/dc devices/other home crap that are largely controlled by relays so that the arduino can know if it was successful?

a small relais of 5 volt dc together with a diodebridge and a shunt resistor (calculate it,like for 1 amp it is 5 ohm use a 10 watt type
same with a simple optocoupler
or a coil with some windings used astransformer

something different is a bulboke cicuit with high freq filter.