Spoilage Sensor

Why don’t we have spoilage sensors on our food, yet? Especially milk and meat. I’m sure they give off some sort of chemically tracable gas; why not a sticker than changes color in the presence of a specified concentration. Not that I’m too lazy to just smell it, but there are times when you can’t really tell. Failing that, why not a standard readable sticker listing how long it may be kept and still be edible?