Say a company has a parking garage for its employees, and they want to track the traffic in and out. So they require that all employees put some kind of tag in their car window, and they have some kind of reader at the entrance to the garage.
What would be the best technology to use in this situation (assuming cost is the largest factor)?
My initial thoughts were RFID tags because they seem to be incredibly cheap if you're only looking to measure over a distance of a couple meters. Are RFID readers that can read over a couple meters a viable solution?