An alert from the US president went out to millions of cell phones Wednesday as a part of a test of FEMA’s Wireless Emergency Alert system. Some people didn’t want to get the message, but they got it anyway. Others who had expected to get the alert didn’t get it at all.

At least four staffers at WIRED with phones on major carriers like Verizon and T-Mobile didn’t receive the alerts. Many WIRED readers reported the same thing on social media. People on every major carrier, with both old and brand new phones, reported not receiving the message. One reader said that AT&T customers in their office didn’t get it while Verizon customers did.

People also made dark jokes, like: “Will I be the first to die because I don’t know the nuke is coming?” But the truth is, there is no need to freak out if you didn’t get the text message. Though FEMA and the FCC have tested the WEA in cities and states before, Wednesday's test was the very first time a nationwide emergency alert has been sent out over text. The entire point was to identify problems with the system so that the FCC, FEMA, and participating cell carriers can work out kinks and improve the warning delivery.

There are many reasons you might not receive an emergency alert on your phone, like if you were out of range of a cell tower, if your phone was off or in Airplane mode, if you have a non-WEA-compatible phone, or if your carrier doesn’t participate in the system. FEMA says on its website, "WEA capabilities were available beginning in April 2012, but many mobile devices, especially older ones, are not WEA-capable." A representative for CTIA, the trade organization that represents wireless carriers in the US, told WIRED that the best way to find out if your phone is WEA-compatible is to call your carrier, as some carriers who participate in the emergency alert system don't offer it on all devices.

But if you were in range of a tower, on a national carrier, and using a relatively new phone, you should have received the message—at least in theory.

"A very important reason to test, and why we initiated it to test locally, state-level, and then ultimately testing at the presidential level, is to discover the actual results versus what should happen theoretically," says David Simpson, former chief of the FCC’s Public Safety and Homeland Security Bureau.

A representative for FEMA told WIRED that all major carriers reported receiving the alert from FEMA’s Integrated Public Alert and Warning System. Once the carriers receive the message from IPAWS, they send it out to their customers using various protocols. Those protocols may differ by carrier or region. “Similarly, there can be variation there with how a Samsung phone interacts with the WEA and how an Apple phone does,” Simpson says.

If you didn’t get the alert, the problem likely has to do with the radio protocols used by your cell phone carrier, and how those protocols interacted with your phone’s firmware, according to Simpson. “There are aspects of how the phones pull the radio access nodes in a 4G environment that could result in a different latency for how the alert gets to different end-points,” he says. Something like network congestion wouldn't come into play, because of how these messages are delivered.

Simpson adds that it’s possible newer phones, which may have been released after FEMA’s most recent local or state-wide tests, may have firmware that reacts unexpectedly to the emergency alert system. “I can only speculate that, because the FCC and FEMA have done many state-level tests and kinks were worked out there, that possibly some of the newest phones didn’t go through the state-wide tests and issues weren’t discovered because the phones just weren’t in production yet,” he says.