A report of what sounded like gunshots prompted Virginia Tech to use its text-message emergency-alert system on Thursday for the first time, but the system failed to deliver all of the messages.

The sounds turned out to have come from cartridges from a nail gun, which the campus police believe someone exploded manually by slamming a trash bin’s lid on them. Echoes of the explosions were amplified because the incident occurred between two high-rise dormitories. But until officials had determined the cause, the university police secured the entrances of the buildings and searched them extensively, even using a dog trained to sniff out explosives.

While that investigation was under way, the university used a multipronged emergency-alert system that it set up in the aftermath of a massacre on the campus in April 2007, when a gunman killed 32 people and then himself.

Officials say that most of the new alert systems worked well. Messages were successfully sent to students, professors, and staff members via university e-mail, on LED display boards in some classrooms, and on university Web sites. But a system designed to send messages to cellphones and other mobile devices, which relies on a product from a company called 3n, failed to deliver to all of the people who had signed up for it, according to university officials.

The 3n system, which is known on the campus as VT Alerts, is designed to send warnings by text message, by voice message, or to non-university e-mail accounts, depending on which method users have chosen. More than 30,000 people affiliated with Virginia Tech have signed up for VT Alerts.

“The system froze up,” Larry Hincker, associate vice president for university relations at Virginia Tech, said in an interview today. “We’re very disappointed, and I am not happy in the slightest at this level of service.” —Jeffrey R. Young