Not sure of the exact specs to this type of sensor, but I remember reading about a guy who did this by winding insulated wire around the mains-wire and measuring the voltage induced in the coil. Sorta like a transformer..
I guess you could wind a wire around the 120VAC mains wire you want to monitor, and measure the voltage coming off this coil with a multimeter. Building rectifier is pretty simple stuff, using 4 diodes and a capasitor. (you'll need one as the voltage coming off the coil wrapped around the mains wire will also be AC).