In case you've somehow missed the news, Samsung's Galaxy Note 7 is being recalled due to a nasty case of occasionally exploding battery. If you're buying a used one, however, you can find out if its safe by looking for the green battery indicator. Photo by Wikimedia Commons.
To denote a phone that Samsung has deemed safe and free from the defect that occasionally caused batteries to explode, the company has changed the battery indicator in the status bar to green. Simply boot up the phone and look at the status bar. If the battery indicator is white, either don't buy the phone or return it to Samsung for a replacement.
If you have the packaging the device came in, you can also identify safe replacements if it has a black square on the sticker with several barcodes on it. You can check SlashGear's post below for more information on how to spot a recalled device or a safe one.