A gadget that pays for itself -- then keeps on paying

SANTA BARBARA, CALIF. -- I've been driving a Prius for a few years, and I'm going to tell you Toyota's dirty little secret. Most of the gas savings come, not from Toyota's sophisticated Hybrid Synergy Drive technology, but from the LCD on the dash that tells you how much gas you're using. Prius hybrids save gas in part because Prius owners drive differently.

If you were to drive a Prius the way most people drive regular cars, you'd probably get about 30, maybe 35 miles per gallon. But most Prius owners -- including Yours Truly -- obsess over that dash feedback and average 45 mpg or higher.

Prius owners know something that people without real-time mileage feedback probably do not know. The way you drive has a radical impact on gas mileage. When you're accelerating quickly in a Prius in stop-and-go traffic, you'll get something like 5 miles per gallon. If you drive really slowly and gingerly, you can get 90.

I know this because I obsess over the car's real-time gas mileage readout. I also obsess over total mileage since last fill-up. My wife and I both drive the car, and we're constantly competing with each other over who can get better mileage. She averages around 50 mpg, and I typically get around 48. When my teenage son drives, he gets around 30.

Gas savings in a Prius is all about the driver, and Prius owners drive differently because we've got constant feedback in our face as we drive.

Here's the good news: Gas savings in non-hybrids is all about how you drive, too. The difference is that most cars don't have a big LCD on the dash telling you how much gas you're wasting as you accelerate.

A gadget called ScanGauge can give you feedback on how much gas you're using in just about any car. There's an amateurish video showing how it looks when you're using it (see below).

Because ScanGauge costs $169, the device will easily pay for itself in gas savings. The more expensive gas becomes, the more you'll save. After you recoup the cost of the device, you'll continue saving money on gas.

I know that I won't convince everyone to buy a ScanGauge, so here's a cheaper technology: your imagination. Force yourself to drive as if there was a scalding hot cup of coffee on the dash right above the steering wheel. Accelerate slowly, coast a lot, and brake carefully. You'll save a fortune on gas.

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