After watching "The Listener", it reminded me of Five-O's sometimes annoying use of "bugs" as a plot device.

The problem with the "bugs" shown in Five-O is that they were far too advanced, range-wise. Bugs existed back to the 1940s in real life, but range and power was always a problem. It was very hard to build a transmission device with a long range, which was meant to fit into a small space. This was especially true during the Five-O run from 1968-1980.

"The Listener" frequently discussed a 2.9 mile radius of the bugs built by villain Cerebrus. We got to see some of these devices, which were quite small. One was actually small enough to be sewn into the victim's clothes without him realizing it!

First off, the 2.9 mile range is nonsense. No tiny device in the early 1970s would be able to transmit 2.9 miles. Furthermore, that range would be very reduced indoors anyway. These devices do far better transmitting outdoors with zero interference. Once you have the subject indoors, there are all kinds of potential forms of interference and metal to where the range drops severely.

It is likely that the bugs used in "The Listener" were supposed to be "RF bugs". At best, these could have reached 1000 feet with no interference, and far less than that indoors. Furthermore, they would die soon enough, and need their batteries replaced. Somehow the villain in the episode was able to listen to these bugs for "months", which is impossible.

In those days, bugs were mostly useful when the listening party would be close by. For example, they could park a vehicle nearby (labeled as a local business or utility), or hide in a nearby room or office. You would not be able to sit 2 miles away and comfortably listen, far from being seen.

There were other episodes involving unrealistic plots with bugs, besides "The Listener".

In general, I like when Five-O attempted to make use of technology of the day to weave into plots ("Computer Killer", anyone?), but the "bug" episodes sometimes really BUGGED me.