"hi-band", from 150–160 MHz; and various UHF bands. Many systems still use conventional FM transmissions for most traffic; others are trunked analog or digital systems. Recently, there has been a move towards digital trunked systems, especially those based around the public-safety standard Project 25 format set by the Association of Public-Safety Communications Officials-International. A minority of other police radio systems, the largest examples being the Milwaukee Police Department and Pennsylvania State Police, use the incompatible OpenSky format. TETRA, the standard in many European countries as well as other places in the world, is virtually unused in the United States. Some states operate statewide radio networks with varying levels of participation from police on the county and city levels: Illinois: StarCom21 Louisiana: Louisiana Wireless Information Network (LWIN) Michigan: Michigan Public Safety Communications System (MPSCS) Minnesota: ARMER Montana: Montana Statewide Interoperable Public Safety Radio System North Carolina: VIPER Ohio: Multi-agency communications system (MARCS) South Carolina: Palmetto 800 Wisconsin: WISCOM It is generally legal in the United States to listen to unencrypted police communications, though some states and municipalities prohibit carrying receivers within vehicles. See also Dispatcher Radio scanner Police code References Law enforcement Types of radios