DURHAM (WTVD) -- It was late Sunday night and Durham homeowner Sioux Watson suddenly heard sirens inside her home.
"It's alarming because you know there's something that's scary that you're supposed to pay attention to but you can't understand it," said Watson.
The sound and voice message that followed was part of the North Carolina Central University Emergency Alert Warning System meant to warn people outdoors about a shooting incident.
Read more about the NCCU shooting.
The campus has three sirens while Duke University has nine. Both campus siren systems are used in the event of an armed suspect, a biohazard, or as a tornado warning. The sound can travel as far as a one-half of a mile, according to the NCCU website.
Duke University says its siren system was tested last Wednesday and has only sounded in recent months because of a tornado threat.
After sirens rang out on the NCCU campus on Sunday night, some frustrated residents took to message boards for more information and to vent about the inaudible voice message from inside their homes.
"It's an outdoor notification system," explained Sgt. Robert McLaughlin with NCCU Police. "They're for people that are out in the open. If you're in your house, you'll hear the siren but you won't understand the words coming out from the speakers."
McLaughlin said the siren's voice message is also difficult to hear inside campus buildings.
That's why he encourages students and staff to register for text alerts. People unaffiliated with the university are also welcome to contact NCCU Police to register for text alerts.
"I'll be glad to sign them up, they just have to be willing to let their phone go off," said McLaughlin. "Our priority is the safety of our students and the security of the University."
McLaughlin says NCCU sends emergency messages through other law enforcement agencies and community groups. Both Duke and NCCU try to alert their neighbors through their websites and social media during emergencies.
"If it was significant enough where we're hitting our alarms, there would be something on our homepage," explained Kyle Cavanaugh, Vice President of Administration at Duke University.
He added that Duke doesn't have a text alert system that's open to the public.
Watson says she's relieved to hear she and her neighbors can register for text alerts and stay informed.
"I find both Central and Duke are fabulous neighbors and we love being adjacent to them," said Watson. "As a neighborhood that's adjacent to the campuses, we want to keep abreast of what's going on."