Question 1: How to lock or unlock channel?Answer: Long press channel "-" to lock the channel, long press again to unlock the channel. Please note, the channel lock/unlock function has the memory function. For example, now the channel lock is open, turn off the radio and turn on the radio again, the channel lock is still valid. RETEVIS RT618/RT18 is new model of license-free two way radio.RT618 has 0.5W power,446MHz factory frequency and it is legal for European countries. RT18 has 2W power,462MHz frequency and it is legal for USA and Canada.Why we need to use the license-free PMR/FRS walkie-talkies?No need to spend time getting a licenseNo legal issue and additional frequency usage fees.Personal use will not interfere with public-service transmissions. Completely Legal License-free Radios Retevis RT618/RT18 walkie talkies is such a professional radio, which you can rest assured to use and no need to worry about the license problem. Five Unique Design Whether you are used to the left hand or right hand, unique dual PTT design, side PTT and front panel PTT, makes it easy for one-handed operation No longer the traditional heavy, big walkie-talkie image, RT618 adopts ultra-thin and ultra-light design, compact and light, more modern and fashionable, very suitable for service industry and personal use.Different from RETEVIS other models, annular breathing light, volume paddle and one-key start design will bring more convenience greatly improve work efficiency. VOX hands-free transmit With VOX function, you can talk directly to the walkie talkies microhome without pressing the PTT button, and the signal will be transmitted automatically once your voice is detected.Note: You need to activate the VOX function through programming software. Micro USB charging USB Charging design offers multi charging choices by power bank, computer in car and so on. Multiple Squelch & Anti-jamming Technology RT618/RT18 has the crystal voice and can keep your communication clearly and smoothly.1-9 grade squelch,50 group ctcss/ 105 group dcs, frequency-hopping will greatly reduce the interference of background noise, shield unrelated calls, give you a quiet call environment. Core companding technology ensure signal quality and filter background noise. Scrambler encryption The scramble feature makes your transmissions sound garbled to anyone listening without the same scramble code.It does not guarantee confidentiality, but it adds an extra layer of privacy. Dependable Coverage Reliable signal coverage made you feel like you are talking with your partner face to face. Usually the call distance in urban areas can reach 1.2Km, and the open area can reach 1-3Km.Note: The actual call distance depends on the usage environment. The fewer obstacles, the farther the call distance. Wide Applications Retevis RT618/RT18 walkie talkie is suitable for a variety of occasions and a variety of people ,can be widely used in big mall, restaurant, hotel, coffee shop, KTV, Bar, warehouse, property management, travel, hunting and so on.