An analog watch shows it's 11:50. But from the inside of the party location, although the drapes are closed, it is clearly daylight. In a few moments, when the first murder occurs, Dan says it was 12:10 a.m. and it is pitch black outside.
When they were sweeping McGarrett's office for bugs, they were just using an ordinary Radio Shack volt-ohmmeter with a rod antenna attached.
The bugging device found in the doctor's office was actually a foreign voltage adapter plug with a circuit board put inside containing a couple of transistors and components. The two prongs on it gave it away.
When the tape recorder taping the sounds and voices from the bug in McGarrett's office, the reels were turning, but the VU meters were not indicating any sound being recorded.