I remembered that once, I had a customer who loves to listen in on his employees. What he did was to have two DSS2060 and a DKT2020D-SD set up on his desk. If he notices any LEDs are on for "too long", he will start to listen in.
Luckily for his staff, the PIOU card always goes on the blink as their earthing system was not good enough. Yeah, and the SMDR cable kept stepped on.
