Hundreds of Verizon outages were reported in the Chicago area Monday morning, with thousands more reported across the country.

According to the website Downdetector, reports of Verizon outages began across Chicago around 7:15 a.m. Monday. As of 9:15 a.m., an increase of more than 700 outages had been reported in the Chicago area, the website showed.

More than 20,000 Verizon outages had been reported nationwide as of 9:15 a.m., according to the website. By 9:30 a.m., that number had risen to more than 70,000, the website showed.

An outage map from Downdetector on Monday showed Verizon outages in several other cities, including Indianapolis, New York City, Atlanta, Cincinnati and Omaha.

Dozens of comments from users on Downdetector stated that their phones would turn “SOS” mode on and off.

As of 9:30 a.m., Verizon had not posted anything on social media about the problems. However, the carrier responded to tweets from several users reporting issues.

“We understand the importance of staying connected and would like to take a look at what’s happening,” Verizon said in several responses.

Verizon did not immediately respond to NBC Chicago's request for comment.

What is SOS mode?

According to Apple, this message appears when “your device is not connected to your cellular network,” but it also means you can make emergency calls using other cellular providers.

The feature is only available in the US, Australia and Canada.

“When SOS appears in your iPhone’s status bar, it means a cellular network is available for emergency calls,” the company says.

Anyone who calls with SOS is automatically redirected to a local emergency number and their location is passed on to the emergency services.

Users can also set their phone to notify emergency contacts after an SOS call with a text message that includes their current location – and updates those contacts if that location changes.

“On iPhone 14 or later (all models), you can even use Emergency SOS via satellite to text emergency calls when cellular and Wi-Fi coverage is unavailable,” explains Apple.