One of the nifty things you can do in Watch Dogs is set up a multiplayer match between someone playing the main game on the console, and someone using the game's companion app on a phone or tablet. Even more impressive: you don't even need to be on the same network for the functionality to work. In fact, you can compete over a 3G connection on the go.
At PAX Prime, Ubisoft showed off how the multiplayer battles work. On the tablet, you can issue challenges to players playing at home. If they accept, they will have to pass through four checkpoints within a time limit.
Tablet players will have full access to the ctOS that controls the city's grid. So, like Aiden, you'll be able to switch traffic lights, trigger traffic blockers, and blow steam pipes--all which can impede progress quite significantly. You'll even be able to drag a helicopter on the screen. Keeping the spotlight on top of the player will send the police chasing.
At first glance, it does seem as though the tablet player may have the advantage. However, smart console players will probably eventually figure out effective countermeasures. One rather neat thing about the companion app is that not only is it free, but it doesn't require owning the game to use. So long as you have a friend playing the game, you'll be able to challenge them--even if you don't have the game.