The resonant circuit connected to the antenna is in the range 100-150Mhz and sources of radio frequency which falls in this range (also with sub harmonics) affect the LRL especially if they are very close and in the house there are many sources of this kind. We can use these sources to test our LRL but my favorite test it's to touch the antenna and check the signal decreases, to do this set the threshold so that the LED is turned on weakly then by touching the antenna the led should go off.
Regards
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