I love sensible technology, which I define as technology that serves a clear purpose, is easy to use for that purpose and which has been designed without huge flaws that severely distract from the purpose. Sometimes individuals who buy the devices that use sensible technology create their own unique purposes for that technology; other times, we're left to follow the manufacturer's intent.

There's a particular thrill when we get to try out true innovations, but due to circumstances, we don't always get our chance. To date, I have not had a chance to ride on a Segway, that unique two-wheeled scooter that is smart enough to balance itself.

Until recently, I didn't have a chance to ride in a hybrid car either. Living in Pennsylvania, where gas prices have only inched over $2 per gallon, I don't know anybody who owns one -- and haven't been tempted to buy one because the price commands a premium over similar combustion engine models.

But in California, where gas prices are well over $2 and sometimes more than $3 per gallon, hybrid cars are all over the place. Perhaps it's the automobile culture in California that requires more mileage per citizen. On a recent trip to San Francisco, I saw more hybrids more often than I could possibly expect to see. I even got to ride in one.

It started when I arrived at the home of my friends, Stan and Julie. We were getting ready to take a short trip. I went out the front door. Julie went into the garage to start the car and back it out of her short, steep driveway where I could more easily enter.

As I stood at the top of the driveway watching her back out, I noticed that the car was silent -- until, as she was already inching up the incline, I heard the sound of the engine starting. It immediately struck me as strange, but interesting. How could a car start while already moving uphill?

The key to the technology is that it runs on electrical current whenever possible, fueled by a big battery. The traditional combustion engine turns on only to accelerate, and to charge the battery. So whenever the vehicle is in battery mode, it runs eerily silently. The advantage to Julie is that she gets more than 40 miles per gallon as she traverses hilly San Francisco.

San Franciscans seem to be adopting hybrid technology happily. We saw a Prius riding through the city every half hour -- driving the streets, in shopping centers, at places of worship; and each time Julie was quick to point to it. Her neighbor bought two.

However, as with most technologies there is a downside -- and in this case, it is not as noticeable as in other cases. The car often rides so silently that pedestrians often don't notice it coming. And, frankly, most people are careless as they wander out into the street, not looking for oncoming cars -- only listening for the familiar sound.

Julie told me how she finds herself being more cautious as she drives her silent Prius in heavy walking areas because she's concerned that otherwise she'll surprise a pedestrian who looks up too late to see her car.

While vigilant drivers such as Julie may be the norm, I'd be curious to see whether less cautious drivers cause more pedestrian accidents driving silent hybrid cars. As a parent, it gives me pause -- even as I love the idea of less engine noise in the passenger compartment and great fuel efficiency. As cars become more silent, we must teach our kids to be more cautious.