A wet floor sign is used to warn people about wet floors and so prevent them from slipping and falling.[1][2] Businesses often place such warnings to avoid negligence charges brought by people on their property.[3] In many countries, if an injury results from a wet floor, the owner of the premises may be found liable for compensatory damages. Many lawyers specialize in such tort lawsuits. Sometimes wet floor signs are not enough.[4] Effectiveness in modifying behavior has been shown to be enhanced when a wet floor warning is also presented aurally every 10 seconds by a tape player.[5] Robotic cleaning equipment can use wet floor signs to know when its job is finished via sonar.[6]