Additional Notes

The default for the capacitors type is ceramic, preferably the npo 1% type or equivalent. But basically nothing critical here. Use any capacitor you have laying arround, but NO electrolytic or tantalum caps. Only if you intend to use this circuit outside the home you may want to select more temperature stable capacitors.

To find the signal on your receiver, make sure there is a signal coming into the microphone, otherwise the circuit won't work. I use an old mechanical alarm clock (you know, with those two large bells on it). I put this clock by the microphone which picks up the loud tick-tock. I'm sure you get the idea... Or you can just lightly tap the microphone while searching for the location of the signal on your receiver.

Source: http://english.cxem.net