The detector can be set for either RF detection (wireless transmitting device) or it can be set for phone tap detection. To set for RF move the switch on the front panel to RF and to set for tap detection move the switch to DET. When set for RF it works exactly like the bug detector and the RF sensitivity screw needs to be adjusted to minimize interference from lights and house hold appliances. Turn the screw counter clockwise or counter clockwise until the AL indicator is barely lit. When the phone tap detector picks up a transmitter the RF light comes on. When set for phone tap detection it will detect any variation in line current including other phones being lifted up on the same line. The DET light comes on and the phone tap has an automatic muting system when a line is tapped.