In the main story case, Investigate the Wiretapper, Yagami gets given a Detector from Tsukumo. This Detector can find the signals of anything illicit bug-wise. But using it may be a bit confusing.
You can access the Detector in one of two ways. The first is by going into your phone, pressing on the Gadgets app, then on Detector. Or press L3 (left thumbstick) in, then press L1, and it'll bring out the Detector—which is the quickest method.
Now it looks very much the same as using Investigate mode and the Noise Amp. The main thing you need to pay attention to is the Detector itself, mainly its screen. If it hasn't found anything, the screen will remain dark, but the second it detects something, it will light up with a single bar of Green.
Green means you're looking in the correct direction, and if it turns to Amber or Red, it means you had the correct direction—now you're looking away from it. Always head in the direction of where the bar turns green.
As you get closer to the signal source, the number of bars will begin to increase. If the bars are amber or red, you are getting closer but not looking in the correct direction. If the bars are green, focus by pressing R2/RT, and if the Examine icon appears, you know you have found it.
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