Residents of which states need a weather radio? It’s a trick question.

Yes, Texas, Oklahoma, Kansas, Maryland and Florida had the highest average number of tornadoes between 1991 and 2010 according to the National Oceanic and Atmospheric Administration. And yes, a weather radio can warn you of an impending tornado, even if the radio is turned off. It will even wake you up in the middle of the night with a loud alarm so you can get to safety. (Many tornado fatalities occur at night when people are sleeping.)

Related: 5 Simple Ways to Prepare for an Emergency

But tornados can and do happen in every state. And weather radios don’t just warn of deadly twisters. They can warn of floods, earthquakes, forest fires, volcanic eruptions and even nuclear power plant disasters. And they give you post-event information (so you know, for instance, when it’s safe to go back outside).

So the answer to “who needs one?” may be: you.

Sure, you can get a weather app for your smartphone that will alert you to a coming storm. But if your battery is dead or you have a weak signal, of if you’ve left your cell phone in your purse or coat pocket in another room, it may not do you a lot of good.

It won’t do you any good if there’s no signal. When Hurricane Katrina reached southern Louisiana and Mississippi, it knocked as many as 2,000 cell phone towers out of commission.

Related: Preparing for a Disaster: Tips from the American Red Cross

What is a weather radio, exactly?

All Hazard logoA weather radio is designed to receive routine and emergency broadcasts from the nearest National Weather Service (NWS) office. It picks up a signal that comes from one of the 1,000 NWS transmitters, which cover all 50 states, adjacent coastal waters, Puerto Rico, the U.S. Virgin Islands and the U.S. Pacific Territories. (Photo: NOAA)

Regular AM/FM radios don’t pick up these frequencies.

NWR broadcasts official Weather Service warnings, watches, forecasts and other hazard information 24 hours a day, seven days a week. In case of an emergency, the NWS will send a 1050 Hz tone alarm before broadcasting the warning on your radio. The alarm will activate the receiver even if the radio is turned off. Not all weather radios come with tone alarms, so make sure to buy one that does.

Several types of weather radios exist, including handheld portable units and desktop and console models that receive Weather Radio as well as other broadcasts.

Related: How to Survive a Tornado

How and where to buy one

Weather radios can vary in price from $20 to over $100, depending on the features they offer. Power can come from solar panels, a hand crank, batteries or A/C power.

Look for a radio with Specific Area Message Encoding (SAME), which allows you to set your radio to receive alerts only for your county. Otherwise you might receive alerts from several counties. You can learn how to program your radio here.

You can buy a weather radio at your local grocery store or pharmacy, such as CVS, Walmart or Walgreens. The American Red Cross also offers weather radio options.

Related: Why You Need an Emergency Plan For Your Pet

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Muriel Vega is a writer with a passion for budget travel and staying safe while abroad. A Georgia State University graduate, she has over 6 years of editorial experience and has written for The Guardian, The Atlantic, The Billfold, among other outlets. In her free time, you can find her baking pies, playing with her two dogs and cat, or planning her next vacation. She spends way too much time on Twitter, one of her favorite social media channels. Her favorite safety tip: Make sure you have all the necessary shots before you go abroad.