JACKSONVILLE, Fla. -

If you were one of the thousands of people awaken by an Amber Alert text message early Monday morning, it may have startled you out of your sleep.

The Wireless Emergency Alert system deployed by cell phone providers last year sends now sends such messages to smartphones.

When Denise Hernandez, a 2-year-old South Florida girl went missing Monday morning from her home, authorities in Collier County rang the alarm -- literally.

The toddler was found safe in a field near her home within a few hours, but thousands got the news of her disappearance in the middle of the night.  But others did not.

"I think if it was my missing kid, I certainly would want everyone to know about it," mother Suzzane Travis said.

"I heard the phone going off, and I went over and it said, 'Amber Alert, check with your local media,'" said James Rouchette, who was woken up by the text message.

Thousands across the state received the alert at 1:42 a.m., but Rouchette said the text left out some critical details.

"It didn't give me any info. It said check with the local news," he said. "If you're going to tell me if there's an Amber Alert, wake me up and tell me what's going on as well."

Hundreds of people went to Facebook on Monday morning and posted their comments about receiving the alert on their phone, leaving others to wonder how come they didn't get the same message in the first place.

So why didn't everyone get the text message? Well, for those who are AT&T customers, the Emergency Alert page isn't supported on their iPhone. Also, to subscribe, customers have to have the iOS 6 operating system, and in settings on the notifications page, users need to scroll to the bottom and turn it on.

For more information about participating providers and how to turn the alerts on and off, visit FCC.gov/guides/commercial-mobile-alert-system-cmas.  Alerts are also available via email from the Florida Department of Law Enforcement.

Opinions vary on whether the system is intrusive or if it's a lifesaver.

"I think it's a bit of an intrusion on privacy," said Bob Smith, who was woken up by the text. "I think missing kids are a major issue, but I think there are other avenues police can take."

"I have no problem with that," another man added.