GM owners can now use OnStar to rent out their cars by the hour through RelayRides.com when they're not in use.

The typical car sits idle for most of the 24 hours in a day. Unless you're a traveling salesperson or a courier, you probably only use your car for a total of two or three hours tops.

Peer-to-peer rentals offer the opportunity to turn those idle hours into cash in your pocket. There are several services that have been pioneering this in select metro areas and on certain college campuses. But the liability issue can be a fuzzy one because we're still in early innings of this business model.

With the GM initiative, OnStar subscribers will be able to list their cars for rent online through the RelayRides website, which will then match up owners with renters. (RelayRides will take 40% of your earnings for arranging the rental.)

The going rate will be about $10 an hour, according to The Los Angeles Times. RelayRides has supplemental insurance of $1 million that is supposed to provide an umbrella on top of your own coverage.

"When [a] reservation [is made,] RelayRides uses global positioning technology to transmit the exact location to the client," The Los Angeles Times writes. "When the renter gets to the car, he or she uses a smartphone application or series of text messages to unlock the vehicle and find a key hidden inside."

Isn't that wild? The beauty of doing this through OnStar is that there's no installation of any system necessary; it's already active in millions of cars.

Of course, I know that not everyone will want to do this. But for some people this could defray the costs of car ownership. Just remember, as the owner, if you get involved with this at any point in the future, make sure the service you choose -- be it RelayRides or another -- has ironclad insurance protection to cover temporary use of your vehicle by another person.

Editor's note: This segment originally aired July 18, 2012.