Starting this September, Smart car owners in Stuttgart will be able to use their cars as mobile addresses for DHL deliveries. Shortly thereafter, the partnership will be expanded to other German cites, such as Bonn, Berlin and Cologne.

The joint delivery experiment uses smartphones, with the car owner and DHL courier communicating with specially designed apps. Smart cars – two-seater subcompact autos made by Daimler AG’s Smart Automobile division – and recent models produced by other manufacturers, allow owners or designated third parties to open vehicles with their smartphones and lock them again after delivery. Daimler-owned car-sharing service car2Go, for example, reserves, unlocks and tracks its rental cars through renters’ smartphones for more than a million customers across Europe and the United States.

The DHL program is the latest in a series of last-mile cargo delivery options designed to meet the needs of e-consumers while avoiding common delivery obstacles, ranging from overenthusiastic family pets to poorly marked addresses. By making it easier to ship packages securely without necessitating the presence of the end-user at the point of delivery, the DHL Smart car program has the potential to bring more customers into the e-commerce universe and expand the purchaser base of e-retailers.

Here’s how it works: Vehicle owners generate a single-use transaction authorization number (TAN), which they enter in the “c/o” box when filling in their delivery address during an e-commerce transaction. For the car drop to take place, the vehicle simply has to be parked in the vicinity of the owner’s home address.

Once the purchase is in, DHL is informed of the preferred delivery location, and the app grants the courier time-limited access to the recipient’s car. The single-use TAN enables the courier to locate and open the vehicle within a set period of time. This turns the car’s trunk into a secure postal box, also allowing DHL to pick up returned shipments. As soon as the trunk closes, the TAN authorizing access is cancelled. Finally, a message is sent via the app to the car owner, confirming that the delivery has taken place.