In a few states it is illegal to use a police scanner while operating a motor vehicle unless you have a license from the FCC or permission from local law enforcement.

Do any of those states consider those laws to apply to using one of those apps?

PS: for those who live in one of those states (Indiana, Florida, Kentucky, Minnesota, and New York) a ham radio license counts, and the entry level ham license (Technician) is not very hard to get.