Two-way radios allow push-to-talk, real-time voice communication to collaborate, coordinate action, and share information or alerts. Handheld radios (walkie talkies) are lightweight, portable devices that withstand more rugged use than cell phones. Vehicle-mount and desktop radios provide communication stations with more output power than handheld radios to talk over longer distances. Marine radios operate on maritime mobile service for communicating while traveling on watercraft or monitoring waterways from land stations. Aviation radios operate on exclusive, civil aviation radio frequencies for communicating while traveling in aircraft or monitoring airways from ground stations. Ham radios (amateur radios) allow long-distance communication among hobbyists, especially during emergencies and natural disasters when cell networks and power grids are down. CB radios (citizen's band radios) are land-mobile radio systems for short-distance communication with nearby travelers.