On VHF radio, most local government and emergency activity occurs in the ranges between 153.785 and 155.98 MHz and between 158.73 to 159.46 MHz. Some larger cities use the ranges between 453.025 and 453.95 MHz and between 456.025 and 467.925 MHz on UHF bands.
Scanners are radio receivers that are specifically designed to pick up local radio transmissions. Many scanners feature scan functions that automatically look for new frequencies and save them to memory banks. Handheld scanners are designed for portable personal use and are typically powered by a battery or an AC/DC jack. They feature small rubber antennas and their primary advantages over mobile and desktop scanners are their portability and small size. However, they have a shorter range than these other types of scanners.
Discovering active local frequencies requires a bit of research. Local hobbyists that partake in radio communications may be a helpful resource in determining active frequencies, as can local electronics repair shops and volunteer police and fire departments. Some standards are in place regarding common frequencies. National Weather frequencies typically reside between 161.650 MHz and 163.275 MHz. Citizens Band frequencies typically are found between 26.965 MHz and 27.405 MHz.
An extensive list of common frequencies can be found at support.radioshack.com/support_electronics/doc66/66366.htm#Q10.