How do you detect a police phone tap?

Answer:
I was once told by a retired FBI agent that if you had 3way calling on a land line & you pick the phone up and call yourself and it doesn't call you right back then someone is listening. Now mind you this was in the 90s so how relevant the information is, I don't know.
First answer by Foughtback. Last edit by Ruckis1. Contributor trust: 0 [recommend contributor recommended]. Question popularity: 10 [recommend question].