Some people on the Verizon cell phone network did not receive the series of Amber Alerts sent out Friday concerning two missing New Hampshire children, and the state is trying to figure out why.

“I have heard from other folks that have a Verizon phone, or who are on the Verizon network, who did not get it. We are talking to Verizon about what happened,” said Mark Doyle, director of emergency services and communication with the New Hampshire Department of Safety.

Amber Alerts are a system to recover missing or abducted children. In New Hampshire, they are usually sent out by the state police and should create a notice on the screen of any cell phone getting signals from a cell tower within the state boundaries, unless that phone has turned off notifications.

An Amber Alert was sent about 4 a.m. Friday asking for the public’s assistance in locating the two children of a woman who had been found dead in her Berlin apartment. It asked people to be on the lookout for a white 2017 Subaru Impreza with a New Hampshire veteran registration V69023.

Police say the children had been taken by their father, 37-year-old Dustin Mark Duren. They were found safe at 10:30 a.m. in Keene and Duren was arrested, leading to a follow-up bulletin canceling the alert.

Amber Alerts are named after a Texas girl,  Amber Rene Hagerman, who was abducted and killed in 1996. It is sometimes said to stand for “America’s Missing: Broadcast Emergency Response” in what is known as a “backronym,” an acronym coined from an existing word.

The national Amber Alert system was created in 2000. On mobile phones, it creates a text message on the screen and triggers what Doyle called “a very obnoxious siren sound” to make sure they are noticed. They also go out on TV and radio and sometimes are displayed on automated highway signs.

The system has since spread internationally. A number of countries, including Canada and Mexico, use the protocol although it often goes under different names, usually those of a child who was a victim of an abduction.

Amber Alerts are part of the Wireless Emergency Alert system, an update that brought cell phones into the nation’s long-standing Emergency Alert System. The system includes emergency warnings, often for severe weather events, which can also be turned off in cell phones, and presidential alerts, which cannot be turned off.