RelayRides and OnStar Inaugurate Car-Sharing Program As of Tuesday, owners of vehicles equipped with an active OnStar subscription can rent their cars through RelayRides, the peer-to-peer car-sharing start-up. The connectivity service, wholly owned by General Motors, should make the car-sharing experience easier, as well as more appealing and secure, according to Vijay Iyer, a spokesman for OnStar. As with any rental through RelayRides, registered users reserve the OnStar-equipped vehicles online. Through a smartphone app, the OnStar service allows keyless access by renters and can foil potential thieves who may pose as legitimate renters through a feature intended to slow or stop the vehicle. The Web-based security measures suit RelayRides, which stopped installing its own keyless-entry hardware earlier this year. OnStar-equipped vehicles follow RelayRides" standard rules and policies. The car owner sets the rental price, on average about $8 an hour. RelayRides provides the owner with a $1 million insurance policy for the duration of the rental and a $300,000 policy for the renter. OnStar expects the partnership to increase uptake of OnStar subscriptions and potentially give lapsed subscribers an incentive to renew enrollment. Mr. Iyer noted in an interview that among the 15 million vehicles on the road equipped with the service, fewer than six million were subscribed. Owners of non-G.M. vehicles equipped with the OnStar aftermarket rearview mirror, introduced last summer, also can use their OnStar service in conjunction with RelayRides, he said. More broadly for G.M. and OnStar, the RelayRides effort tests the viability of partnerships to develop applications for OnStar-equipped vehicles. "A big part of this was testing the technology and providing access to core vehicle features to an outside developer," Mr. Iyer said. It's a lot more complex than developing an app for an iPhone. OnStar plans to open its application developer program to other parties later this summer, Mr. Iyer added. Subsequent versions of the app would, like OnStar's Family Link, help an owner track the location of a vehicle, allow a user to remotely monitor a home's energy use and send a text message when fuel levels or tire pressure are low. For its part, RelayRides, which recently began offering its car-sharing service nationwide, expects the partnership to increase membership and differentiate its offering in the crowded car-sharing market. Both companies have an interest in making the relationship work, as G.M. Ventures, the automaker's venture capital group, invested in RelayRides last year. Terms of that investment have not been disclosed.