Run, walk, bike your way to a full charge

It's the digital kiss of death -- the moment your cell phone dies, right in the palm of your hand. Now, three engineering grad students think they have a portable solution, and they're banking on kinetic energy for the next trend in wearable technology, CBS News' Adriana Diaz reports.

"Everybody's had an issue where their smartphone has run out of power at the worst possible time," 25-year-old Tejas Shastry said.

That worst possible time is during his nightly call with his fiancee, Jennifer Hemesath. They're now mostly long-distance after she moved from Chicago to Iowa for medical school.

She said he's notorious for having his phone die at the worst times.

"He really is, and I mean, he's a busy guy," Hemesath said.

Shastry's busy creating AMPY, a device he and fellow Northwestern Ph.D. students Alex Smith and Mike Geier invented in class. They say it's a cure for the dead cell phone, turning energy from a person's physical movement, called kinetic energy, into battery power.

"We knew there were ways to transfer physical kinetic energy into electrical energy," Smith said. "The secret for AMPY really came from taking somewhat existing technology and shrinking it into a form factor that can fit right here in your pocket."

From your pocket or your purse, AMPY charges as you move throughout the day. When your battery goes red, connect the device to your phone and re-juice at the same speed as a wall plug.

The trio claims that running for 30 minutes, cycling for an hour or walking 5,000 steps provides enough people power for one hour of active smartphone use.

While there are other products on the market, Smith said they're about the size of a paper towel roll.

"They will couple to your motion and capture your energy, but they're all big and bulky, and you wouldn't really want to fit them into your life," Shastry said.

That's why AMPY's small size has big appeal. In fact, more than 2,500 pre-orders have already been placed, many through the crowd-funding site Kickstarter, which has raised over $300,000 for the device.

While the team is still building prototypes with a 3-D printer on campus, they expect to mass produce this summer. But at nearly $100, some wonder if AMPY's convenience is worth the hefty price.

"If AMPY can deliver on what it promises, it will be very impressive, but there's that cost factor, especially when you can get a spare battery for $25 or less," CNET senior editor Bridget Carey said.

For consumers who often forget to charge that spare battery or portable charger at home, AMPY provides an on-the-go way to power up in a pinch.

"It's juice for the end of the day when you need it most, if you will," Smith said.

That self-generated juice could translate into more uninterrupted phone calls to support long distance love.

"He uses his phone a lot and it does die easily," Hemesath said. "But it's been nice with AMPY because it hasn't been happening as often."

She said she's actually noticed a difference since the tech has been around.

"There were times when he would call me; he would say 'I'm calling you with AMPY right now because my phone is dead,' and I was like, 'Man, I'm glad you invented that,'" Hemesath said.

It's an invention that could help the world's 3.5 billion cell phone users cut the cord and move toward battery independence.