The humble dog collar might seem like something that couldn't really be improved upon in any significant way, but ... what if you combined it with a leash? Well, what you'd end up with is the Supercollar. It's a polypropylene collar, with a three-foot (0.9-meter) retractable leash built into it. Perhaps not necessary in all situations, but there a few where it might come in handy.
The Supercollar's leash consists of two coated steel cables, which run from two retractors (one on either side of the collar) to a single rubber handle. When not in use, the cables roll up inside the retractors, and the handle is locked to the collar. By unlocking the handle and pulling it out, the dual-line leash is revealed.
Each cable reportedly has a breaking strength of over 100 pounds (45 kg), and the retractors are said to be waterproof with "dirt and debris flushing technology."
For everyday dog-walking, this device probably isn't going to usurp the traditional leash-and-collar anytime soon. It looks like it would be simpler just to use a regular, slightly longer leash, and in fact the Supercollar has a D-ring where one can be attached. For things like off-leash parks and car trips, however, where a leash isn't strictly necessary but is still good to have close at hand, it could have its merits.
The Supercollar is available online, for US$49.95 plus shipping.