If Mayor Menino really wants Boston to lose 1 million pounds, maybe he should persuade supermarkets to use the Lambert Shopping Trolley Handle, a nifty gadget that tells you if the contents of your shopping cart are more or less healthy than average.

The device, developed in the UK, also contains a bar code scanner, and has a series of LED lights that blink upon scanning to indicate various variables. For instance, it can be programmed to blink based on the salt content of the item, or its food miles, as in the video below.

But more interesting than that is the simple smiley face display in the center of the handle that smiles if your cart is better than a norm – say the average calories per cart, or food miles or whatever else you’d like to imagine – the face is smiling. If it’s around the norm, it’s a straight face. And if it’s worse, it’s frowning.

This is appealing because of its simplicity and because of its direct comparison to others. Just like OPower has had some success showing customers their energy use relative to their neighbors, this simple comparison has the potential to encourage healthier purchases.

And as Ariel Schwartz reports at Co.Exist, the researchers behind the device believe they have some evidence to back up their idea:

Would the technology actually influence grocery store decisions? According to the researchers behind the device, yes. They sent 18 U.K. shoppers to a well-known chain grocery store with shopping lists and carts outfitted with the Lambent handle. They found that when shoppers used the device, 72% of the products they bought had a lower mean food mileage than products bought when they went shopping with a normal cart.

A small sample size, but encouraging nonetheless.

Though the video below spends a lot of its time bashing mobile apps that do similar things, I don’t particularly care if this kind of technology is incorporated via mobile devices or shopping carts. I would, however, like to see it integrated into payments, and that’s where I think mobile makes a lot of sense.

Done right, this kind of technology can work as a kind of commitment device, where the shopper commits ahead of time, in a moment of strong will, to staying within certain boundaries. So rather than just seeing a frowning face nudging you not to buy such unhealthy food, you could imagine opting into a system voluntarily that doesn’t let you check out of the store if your cart falls below the average for healthiness.

We’re not there yet. But this judgey shopping cart is a step in the right direction.