An exploded cartridge from a nail gun produced sounds similar to gunfire near a Virginia Tech dormitory Thursday, briefly scaring a campus still scarred from mass shootings last year.

The scare was the first use of the university's revamped crisis alert system. Virginia Tech added text messages and other ways of warning students of possible danger to its system of e-mail alerts after gunman Seung-Hui Cho took 32 lives before turning the gun on himself.

The results were spotty: While an initial text message explaining police were investigating potential gunfire was successful, text messages that explained the sounds were not gunfire did not go through on mobile phones. The problem was traced to the service provider in the mountainous area, university spokesman Larry Hincker said, and school officials have asked the vendor for an explanation.

"We attempt to use as many channels as possible to notify the community of emergency situations," Hincker said in a statement. "We regret that the one system not under our control failed to work as expected."

Police secured Pritchard Hall around 1 p.m., and searched every room in the 1,000-student dormitory. They reopened it two hours later after finding no evidence of gunshots.

The school sent out a campus alert saying police were investigating "reported sounds of gunshots in Pritchard Hall" before police determined that the sounds came from an exploding cartridge from a nail gun that had been set off near a trash bin.

Police responded to the dormitory within three minutes of the report, Hincker said, and the campus was alerted with a series of messages sent to e-mails, to cell phones, on the school Web page and to classroom message boards.

Several students said they got alerts both by e-mails and text messages. About 30,000 students, faculty and staff on the 28,000-student campus subscribe to the emergency text message system, and 70 percent of them wanted that to be the primary way they are notified about potential danger on campus.

"I was actually very impressed by how quick it was," said Adam Parker, a sophomore who got an e-mail and two text messages.

But freshman Lauren Dalton said, "By the time I got the alert, it was over."

Officers found an exploded cartridge from a power nailer used in construction near trash bins nearby. Police theorized that someone caused the construction shell to explode, possibly by slamming the lid of a trash bin, and the sound echoed.

Only the dorm was locked down because witnesses reported hearing the sounds coming from the direction of that building, Hincker said.

There are several construction projects nearby, campus police spokesman Lenny Session said, and authorities were looking for two men who apparently set the cartridge off.

Mina Sharobim, a sophomore resident adviser at Pritchard Hall, said he didn't hear any loud noises, but spoke with police officers who were conducting the building search. He was satisfied with the response: "Especially with the things that have happened here, you never can be too careful."