On an email list I belong to a member was recommending this gas-saving device. It apparently works like the fuel economy gauge that many cars have in them already but supposedly is more accurate. It helps you save gas by helping you adjust your driving habits to be more fuel efficient. The reviews I’ve read on the web seem good but at a price of $169.95 it would have to save a lot of gas to be worth it. It also has other features but since it is only for 1996 or newer cars it won’t work for me so I haven’t looked into them too much.
Another possible device for those with older cars is a vacuum gauge. There are some of them made especially as mpg gauges but you can get regular vacuum gauges for as little as $15. These aren’t very accurate at telling your instant mpg but they are good at helping you drive more efficiently. Since these are much cheaper than the ScanGauge it shouldn’t take nearly as long for you to make back the purchase price.