Is there a reason people can't just have seatbelts of some type for that? By the inverse square law accuracy should be better at close range, cutting out at 10

Is there a reason people can't just have seatbelts of some type for that? By the inverse square law accuracy should be better at close range, cutting out at 10 to 30 feet but not 0 to 6 feet should be possible, especially with UWB, and even moreso if the fob detects water directly.