Farmyard Driveway Vehicle Sensor

Hi,
I'm posting on behalf of a neighbour who asks if anyone knows of a low-cost ground sensor or beam sensor that can be positioned on a farmyard driveway and will alert the house occupants of vehicles on the driveway? Not looking for complicated CCTV or expensive gadgetry - a simple unit would suffice. The distance from driveway to house is about 30 metres. I've searched on-line but would prefer advise from anyone with direct experience of any such devise.
Thanks in advance

You don't say what you consider expensive gadgetry, but you're going to need some level of gadgetry to achieve what you're trying to do. There are three options I can think of, a beam break sensor, an ultrasonic sensors as used for car parking sensors, or a ground induction loop.

The ground induction loop is likely the most simple and robust. These are the kind of sensor they place under the road surface at traffic lights (and that so many cars seem to drive past before stopping for some reason!)

I've no experience with this company, and there are many others, but [broken link removed] will give you an idea of prices.

a very cheap option here