Land mobile radio systems (LMRS), also known as public or private land mobile radios, are wireless communication systems designed for users in vehicles or on foot. They're primarily used by emergency services, public works, and businesses with large fleets or field staff. These systems can operate independently or be linked with other networks like the public switched telephone network or cellular networks. Walkie-talkies, officially known as handheld transceivers, are portable two-way radios. These devices were developed during World War II by various engineers, including Donald L. Hings, Alfred J. Gross, and teams at Motorola. Post-war, they became common in public safety, commercial, and jobsite work. Key features include a half-duplex channel, which allows one radio to transmit at a time while any number can listen, and a "push-to-talk" switch for starting transmission. Walkie-talkies, typically resembling a large phone handset with a top-mounted antenna, have built-in speakers that allow both the user and those nearby to hear. They can communicate with each other, as well as with vehicle-mounted or base stations.