What are those commercial gates sensing when you drive up to them to exit a business or gated community?

Question

When I exit my work at night, the doors can tell when my car pulls up. Is it weight sensors in the ground, a laser or something more advanced?

Answer 1

Sometimes, It's magnetic inductance when a sufficient amount of metal is passed over the sensor. Other versions work on weight.

Answer 2

You can learn all about it at the link below. Inductive loops (electro-magnets) sense iron, then trigger the timer controlling the light or gate. For more, see the link.

Answer 3

It is reading the inductance generated by a coil of wire buried in the road.