... enviroment for construction site 2. Improve level of construction Lift buzzer button system can show 3 groups of number at the same ... : ≤20mWTransmitted Distance>1000m in open area Warranty:12 MonthsFAQApplicationsWireless calling system can be used in restaurants, hotels, hospitals, tea house, ... know who's calling need and go to there . Lift buzzer button system can show 3 groups of number at the same ...