"Why, I would use motion sensor with " blinders" to sense car on my driveway, close relay, and to turn ON carport and walkway lights and even have timer to turn them OFF".
Since this circuit detects large iron objects as cars or trucks and is interesting to me I tried it in simulator.
Locate the transformer, it is 600 ohm to 600 ohm audio coupling transformer. Right of transformer is Colpitt's oscillator at 10 kHz. Left of transformer is Maxwell - Wein bridge with capacitor and variable resistors to balance out inductive phase shift.
The induction coil at low left (shown as 10 mH. ) is 50 turns of 26 gauge wire wound on 50 inch form and not deeper than 8 inches in driveway. This coil in driveway detects large iron mass to unbalance normally balanced 10 kHz. bridge sending AC output to activate above circuit to close relay to light system. Added to unbalance system in simulator is bottom switch,1 uf capacitor, and 1 kHz generator.
Some circuit balancing skills would be needed to make circuit operational.
