About 20 years ago, my birding partner and I had 8 EASO's in 20 mins. on Cardinal Street on Lehigh Mountain, Salisbury TWP., Lehigh County. Some other friends and I tried again on Tuesday: EASO 0, GHOW 0, and BAOW 0, besides play backs from a cell phone app (Audubon), headlights on, staying in car as a blind, etc. Not even a call note.
The time we saw the 8 was November. Maybe now that they are beginning to breed, it possibly explains the silence. I feel real bad, and will do it only in the fall next time.
For indoor-car/outdoor acoustics, try baby monitors from the dollar store if on a budget. Some of the brands are not that bad sound-wise. Someone told us about these on the eBird group when they had one.
However, if you have some bucks, the posted electronics method sounds better. Like with optics, you tend to get what you pay for.