Weight Sensors

Based on the news of many children dying because they are being left in hot cars, I have an idea that can prevent this from happening in the future.
I think that Sensors should be installed in back seats same as those that alert you when your seatbelt is not fastened. Maybe some sort of weight sensor that when the driver's door is opened, a notification bell or signal of some sort can be heard or maybe a sensor that can prevent the ignition from being turned off if there is a presence in the back seat. This May not always work if you have cargo but if they child is strapped in, then a belt sensor should do the trick. If this can be installed moving forward and-or be installed in all family vehicles, it would make a world of difference.
Lets save our children