In an emergency, people sometimes call the police. With Wentzville's new emergency notification system, the police call you.

In August, the city activated the Wentzville Information Notification Delivery system, or WIND. It allows the city to deliver emergency announcements to residents via telephone, text messages and email. Residents can register for the free WIND system through a link on the city's website at www.wentzvillemo.org.

Interim Police Chief Kevin Pyatt said the city is waiting to finish tweaking the system before launching a major public awareness campaign. But the system has already proven useful, he said.

On Nov. 16, police were gearing up for a full-scale search after a 9-year-old girl had been reported missing for two hours. Parents called police in a panic, saying the girl went on a bike ride and never returned, Pyatt said.

At 5:30 p.m., police used WIND to send a message to the geographic areas where the missing girl most likely would have been seen. WIND uses a computer-generated voice to deliver messages by telephone. In less than one minute, 98 percent of the people in the specified area received the message, Pyatt said. In less than two minutes, people were calling the police, asking for more information about the girl.

Police were organizing at the parents' house when a neighbor drove up and dropped off the girl. She had been playing with a friend, Pyatt said. Whether the neighbor was responding to the WIND message was not certain, but Pyatt credited the system with helping mobilize the community to respond to an emergency.

It was the second time Wentzville had used WIND. Shortly after activating it in August, the city used the system to tell residents they would temporarily lose water service while the city repaired a broken line.

WIND replaced the city's old Reverse 911 system, which it had used for more than a decade. Pyatt called the Reverse 911 system "antiquated." It required the city to maintain a massive server and monitoring system, and pay for additional phone lines. Reverse 911 could notify only eight people at a time, Pyatt said.

WIND can notify hundreds within seconds, he said. It is Internet-based, so it requires no additional phone lines or hardware.

The city contracts with California-based Everbridge to operate the system and pays the company about $10,000 annually, Pyatt said. The city does not share residents' personal information with Everbridge, he said.

WIND sends emergency messages to all listed phone numbers. Residents can register to receive messages on unlisted numbers and cell phones. They must register to receive text and email messages. If they choose to opt out of the program, they will still receive emergency alerts on listed phone numbers, but will not receive messages via any other method.

Residents can select what categories of messages they want to receive. Besides emergency alerts, they can sign up to receive notifications about community events, such as neighborhood watch meetings.

If they do not have Internet service, they can sign up for WIND using a paper form available at City Hall, 310 W. Pearce Blvd.

Though WIND is aimed at Wentzville residents, nonresidents also are free to sign up, Pyatt said. It could be useful for people who live outside the city but have relatives, businesses or property in Wentzville, he said.

O'Fallon used to have a Reverse 911 system but discontinued it. O'Fallon spokesman Tom Drabelle said not many residents signed up for it. It was an old system that called one person at a time, he said. Now the city uses Twitter as its primary notification system. About 2,500 people follow O'Fallon's tweets, he said.

St. Peters uses a text message system. According to information on the city's website, www.stpetersmo.net, residents and nonresidents can sign up to use St. Peters' free system, receiving text messages about public safety, crime alerts, Amber alerts, attempted abductions, traffic disruptions, road closings and last-minute event postponements. The St. Peters system is for urgent messages only, not routine information, according to the website.