all-sun Ultrasonic Leak Detector & Transmitter Air Water Dust Leak Pressure with Headphone Accessory Kit LED Indication In Active mode, Both EM282-R and EM282-T were fully functioned. In passive mode, only EM282-R is used.  Passive mode can be to detect and locate leaks in pressure and vacuum systems. These leaks can generate ultrasonic emission which can be detected by EM282-R EM282-R EMR282-T