States are required to keep tabs on registered sex offenders.
That means states need to be informed about where sex offenders live and where they've found a place to call home.
For example, California's Megan's Law requires law enforcement agencies to track where sex offenders live and provide community notifications.
Individual states decide what information is available and how the public can access it. In some cases, the information is available through a toll free number, the police station, newspapers or a public sex offender web site.
Most states have residency restrictions for convicted sex offenders, and as a result, after sex offenders leave prison they are often packed into the limited neighborhoods where they may live.
But some communities don't believe that state law goes far enough and have created their own ordinances that restrict where the convicted sex offenders can live.
For example, in New Richmond City, Wisconsin, the city council is currently considering a new safety zone ordinance. It is an effort to provide law enforcement with a tool to arrest sex offenders who may be trying to find future targets. The safety zone would be set up around schools, parks and day care centers.
In some cases, the strict residency restrictions have caused more issues than they have solved. Many sex offenders cannot find housing in urban areas across the state and often are forced into homelessness.
As previously discussed, in California law severely restricts where sex offenders are allowed to live after they are released from prison. Those convicted of rape or child molestation or even misdemeanor indecent exposure cannot live within 2,000 feet of a school or a park under its provisions.
Currently, the California Supreme Court is looking at the cases of four ex-convicts as it considers whether the residency restriction contained in California's Proposition 83 is so broad and intrusive that it violates the constitutional rights of registered sex offenders, the San Jose Mercury News reports.
Outside of California, more than 20 states have adopted similar provisions, with courts taking a mixed view of whether they pass legal muster.
Critics have said that residency restrictions often make it more difficult to track registered sex offenders who declare themselves transients.