It might not be able to monitor an entire city, but Steve Hoefer's brilliant sonar glove will at least let you get to the bathroom at night without stubbing your toe, thanks to an ultrasonic emitter and haptic feedback.
If you're looking for an awesome do-it-yourself project this weekend—besides creating an epic Superbowl feast—Make has posted all the necessary components and steps needed to build Steve's Tacit Haptic Wrist Rangefinder yourself. It won't turn you into Batman overnight, but it's a great first addition to your utility belt.
Using an array of ultrasonic emitters, which are of course inaudible to humans, the Tacit glove measures the distance to objects and walls in a room. As you get closer to something, a set of servo motors press harder on either side of your wrist letting you know where an object or obstacle is. It seems to work great, unless you're trying to navigate a hangar full of stealth fighters at night. Then you're screwed. [Make]