Saw this tonight on the local news:

"Washington D.C. & Md. - If your phone suddenly begins to beep and buzz loudly tomorrow morning, do not be alarmed. Millions of people across the DMV will be affected by Thursday’s Wireless Emergency System.People are warned that on many phones that test may come across as being extremely loud or startling. A text message will also be sent to your phone announcing the test.

Montgomery, Prince William and Prince George’s counties will all be involved in the test as will the Frederick and Loudon areas.

The test is set to last from 10 a.m. to 11 a.m.

localdvm.com/news/i-270/loud-phone-test-set-for-thursday/1102085227