Credit: Bethesda Beat file photo

Don’t be surprised if your mobile phone suddenly emits a loud noise and starts vibrating between 10 and 11 a.m. on April 5.

Montgomery County is one of 20 jurisdictions that is participating in a region-wide test of the national Wireless Emergency Alerts system. The live test will be the first time the system is used regionally and the test alert is expected to reach about 5.2 million people.

County residents are expected to receive a message that says, “A test of the Montgomery County Wireless Emergency Alerts System. No action required.” The message will “trigger a loud (somewhat annoying) notice and will cause the phone to vibrate,” according to the county.

The audio signal and vibration will be repeated twice.

The system is overseen by the Federal Communications Commission, which allows national, state or local government officials to send public safety-related alerts. People do not sign up to receive the alerts, instead the system enables government officials to send the alerts to phones if the person’s wireless carrier participates in the program. Carriers such as AT&T, Sprint, T-Mobile and Verizon distribute wireless alerts, according to the technology news website Recode.

Jurisdictions participating in the alert are using geo-targeting to try to reach only people inside the given jurisdiction, such as Montgomery County. However, the county warned that people travelling through counties or cities in the region during the day of the test may receive alerts from multiple jurisdictions.

The test is designed to help the county, other jurisdictions and the federal government make alert messages more targeted and efficient during a real-life emergency such as severe weather, a terrorist threat or a chemical spill.

Recode noted that officials in Texas and New York have been unhappy with the current alert system after it was used in Houston during the flooding that followed Hurricane Harvey and in New York City after a bombing in Manhattan in 2016. In Texas, officials complained the alerts weren’t targeted enough to a specific area to be particularly helpful. Leaders in New York said they’d like the ability to also send multimedia—such as a suspect photo in the alerts.