The Albrecht ATT/ATR400 20er is a professional digital tour guide system designed to deliver crystal-clear audio for group communication in a variety of settings such as guided tours, factory visits, museums, and training sessions. This complete 20-piece set includes one ATT400 transmitter and nineteen ATR400 receivers, all operating on the interference-free 2.4 GHz ISM band, which is globally usable and license-free. Each device is compact, lightweight, and user-friendly, featuring a standard 3.5 mm audio jack for compatibility with most headphones. The transmitter includes a clip-on microphone for hands-free speaking, while the receivers come with hygienic in-ear headphones. The system ensures clear sound transmission over distances of up to 200 meters, making it highly effective even in large or noisy environments. One of its key strengths is long battery life—each unit can operate for up to 18 hours on a full charge. The set is stored in a sturdy carrying and charging case, making it convenient to transport, organize, and recharge all units simultaneously. The system is ideal for professional use where reliable, long-range, and high-quality communication is essential, while also ensuring comfort and ease of use for both guides and participants.