They got tired of lugging and wrestling with their bike locks, so they stopped riding entirely.

Therein lay the germ of an idea for a group of seniors majoring in mechanical engineering at the University of Pennsylvania: Why not devise a bike lock you don't have to carry?

This is senior-project presentation season for engineering students at schools such as Penn and Drexel University, when teams are evaluated on their ability to solve problems with elegance and simplicity.

Diagnose the flu in less than 10 minutes, at a cost of $3. Treat spinal cord injuries with stem cells. Write software to allow people with Lou Gehrig's disease to control their home appliances.

And for those who travel on two wheels, there is PubLock: Secure your bike to a rack with a wave of an electronic key card.

The range of creativity is enough to make one believe that a chunk of the world's problems could be solved by teams of 21-year-olds, a string of all-night brainstorming sessions, and cold pizza.

Few, if any, of the projects end up on the market, as students tend to go their separate ways after graduation. But at Penn, professors say, an increasing number of teams each year file disclosures to preserve their patent rights.

At Drexel this year, at least one group already has lined up a client. Students designed a stormwater retention dam for the Unitarian Society of Germantown, which church officials aim to build after securing a grant. "It's fantastic," said Bill Blasdel, cochair of the building and grounds committee for the church on Lincoln Drive.

Another Drexel team is retrofitting a van with equipment for mobile testing of air quality in the Marcellus Shale region.

Even for projects that do not make it beyond the prototype stage, the process marks a full-strength dose of the real world, said Beth Winkelstein, associate dean for undergraduate education at Penn's engineering school. That includes coming up with an idea, setting and meeting goals, evaluating the results, and presenting them.

"There's really nothing different from what they just did over the last seven months and what they would be expected to do if they get an engineering job," said Winkelstein, a professor of bioengineering and neurosurgery.

At Penn last week, the top three designs from each of six engineering departments went head-to-head in a school-wide competition. A panel of alumni judges listened as teams of dark-suited students took to the stage of the Wu and Chen Auditorium in Levine Hall, presenting their findings and conducting demonstrations.

Among them were Joe Hill, Alex Neier, Joe Polin, and Justin Starr, the team that developed PubLock.

They built a prototype of a rugged, retractable chain lock that would be permanently attached to a bike rack; riders could open and close the lock with a card that uses radio-frequency I.D. technology.

The students envision hundreds of such locks being installed on a college campus, usable by anyone with a personalized RFID card. Once someone secures a bike in a particular lock by waving a card in front of the mechanism, it can be unlocked only with the same card.

(RFID cards will be part of Philadelphia's bike-share program, slated to begin next spring, according to B-cycle, the company supplying the equipment. Similar technology is widely used to unlock doors in office buildings.)

Bruce Kothman, the senior lecturer in mechanical engineering who advised the team, praised the students' work ethic. "These guys were running the whole time," he said.

They did not manage to snag a prize in the school-wide senior design competition, however.

After hearing presentations from the 18 teams, judges announced three honorable mentions and three top prizes, each drawing loud whoops and applause.

First prize went to the developers of the rapid flu test: Camilo Bermudez, Liz Feeney, David Gabrieli, and Leah Suttner.

Gabrieli said rapid tests were on the market already, but they had "false negative" rates of up to 50 percent, meaning someone with the flu was incorrectly said to be flu-free.

The team's technology, which built on the work of their adviser, assistant bioengineering professor Arjun Raj, reads cell samples using laser light and is close to 100 percent accurate in lab tests, Gabrieli said. The Raj lab plans to try the test on cells from actual flu patients during the coming winter, he said.

"We thought our project was very well thought-out," Gabrieli said. "But none of us really expected to end up winning it."