How 2.0

The explosive C4, a favorite for everything from demolition to terrorism to action movies, is in fact one of the safest explosives. How can an explosive be safe? If it’s hard to set off by accident. C4 is so stable that you can light it with a match (it burns but does not explode) or shoot it (it splatters but does not explode). To go bang, it requires a detonator that produces both heat and shock.

At the other end of the spectrum are mixtures that ignite simply from being scratched or knocked. There are obvious challenges in mixing, storing, and handling these substances so that they explode only when intended, yet they’re surprisingly common.

I tried to love Amazon's amazing e-ink electronic book reader, the Kindle, I really did. But I wanted a device that had full color and a higher-resolution display and that didn't limit the content you can view on it. So instead of shelling out $300, I decided to make my own version using a tablet PC -- basically a computer with a stowable keyboard (or no keyboard at all) that you mainly control with a stylus and touchscreen.

When Nintendo debuted its DSi game console earlier this year, it closed the loopholes hackers had used to run homebrew applications—unofficial software distributed freely on the Internet—on its predecessor, the DS Lite. But hackers soon found holes in the DSi’s software too, and now DSi-compatible “flash carts,” specially modified cartridges that allow you to run custom code, are coming to market.

I can’t stand diamonds. No, really, they just tick me off, because nearly everything about them is a lie. Diamonds are neither rare nor intrinsically valuable nor uniquely romantic. Those are ideas invented by the diamond industry. And no, despite what the ads tell you, diamonds are not forever. They are flammable and will burn brightly with a little help from a torch. This makes perfect sense when you consider that they are made of pure carbon, which reacts with oxygen to form carbon dioxide (“reacts with oxygen” just being another way of saying “burns”).

You can. And now that Google has launched its Google Voice service (google.com/voice), it’s free. At press time, the service was invitation-only, but when it becomes more widely available, here’s how it will work: You get a new universal phone number with your choice of area code, along with a Web-based inbox to manage your voicemail, text messages and call history.

Who needs brakes? When you’re converting a junk-stuffed shopping cart into an electric joy-ride-mobile, they’re the last thing you worry about. MIT undergrad Charles Guan’s LOLriokart—the name is a mash-up of Web and videogame-speak—grew out of his membership in the MIT Electronics Society, a student engineering club. With no plans to build a vehicle, he looked around the club’s shop and spotted the shopping cart, some discarded wheels and an electric engine normally used in high-performance golf carts.

One word: performance. If you’re a gamer, a designer or a movie lover, you’ll need a full-fledged laptop. Even low-end models like the $550 Gateway MD have large screens and feature fast processors and lots of memory that let you easily run multiple programs or powerful apps like Photoshop. To get fast enough graphics for Blu-ray movies or games, though, your starting price will go up.

It’s the middle of the night, when suddenly you’re jarred awake by your ringing phone. It must be urgent, so you can’t waste time—or worse, miss the call—fumbling around trying to find the receiver. Instead, simply touch your hand to the top of your bedside table to answer the speakerphone. The secret is a stud finder (stuffed into the drawer of the nightstand). With a few modifications, it can sense when your hand is near it and activate a switch connected to your landline.

I remember seeing a demonstration of a seemingly magic process at an engineering open house decades ago, in which a soft metal bit carved detailed shapes into far harder metals. It's called electrochemical machining (ECM), and it's so simple in principle that you can do it at home with a drill press, a battery charger and a pump for a garden fountain.