It turns your phone into a mobile police scanner, and it's illegal for most people to have. Byron Fenoglio of Carmel, Indiana uses it.
"That gives you access to almost any police scanner in the United States," said Fenoglio.
Eugenea Bare of Muncie also uses it.
"I keep track of the weather. If there's a tornado, I know which way to go to get out of the trailer park," she said.
But the app, for Android and the iPhone, is running up against the law, at least in Indiana. Police don't want you to have it and state law say that the average person can't.
"The statute is that if it's being used as a police radio, that's illegal to have," said Det. Jim Johnson, Muncie Police.
By law, you can listen to a police scanner at home or in a business, but nowhere else. And there's a reason. Police are worried about the popularity of the app because criminals are using it. The most recent incidence is in Muncie during a robbery of a pharmacy.
Investigators say that while Brian Franklin was allegedly robbing the store, Matthew Hale was in the getaway car monitoring the Muncie Police on his smartphone.
Hale was charged with robbery and unlawful use of a police scanner, which is a misdemeanor.
"We don't want them to be able to use that to assist in their crime and that's what they were using it for," said Det. Johnson.
But what about law-abiding people like Eugenea and Byron, who had no idea that the app on their phone could place them in jeopardy?
"Well, really, I'd rather be safe than anything else. I'd rather have my kids safe," said Bare.
While the app police aren't apt to charge most people with a crime, they want you to know it's illegal in Indiana and that criminals are also listening. There are ten exemptions to the law but they don't apply to the average person.
Some police agencies also believe that the penalty for breaking the law needs to be stronger. They say if you have that app on your phone, delete it. Laws governing mobile and personal home police scanners vary state by state, but there are some federal laws enforced by the FCC.
They include rules that ban you from using information you hear on a scanner for personal gain. For example, a taxi driver cannot listen to a competitor's dispatch and then race to pick up the fare first. It is also illegal to use information you hear to help you commit a crime.
It is illegal to disclose information you hear to other people, meaning if you have a scanner in your home, you are not allowed to tell other people what you hear.
(Copyright © 2011 NBC Universal, All Rights Reserved)