I started writing this as part of my series on Star Trek continuity, but when it took on a life of its own I decided to separate it out.
Few technologies have suffered so much for the sake of the plot as the internal sensors of a starship. Even the same starship in the same series might have radically different performance from episode to episode, depending on how difficult it needs to be to find the latest alien intruders.
There are times when the sensors are clearly top of the range Starfleet technology. Within seconds, bridge officers can scan for life forms within and without the ship, sometimes even several light years away. They can report on the species and sex of organisms both living and dead, and occasionally even lock onto them with the transporter and beam them out of danger.
But at the slightest hint of trouble, the sensors go haywire. Throw in a little radiation or interference, and suddenly the sensors stop working. Numerous materials encountered by Starfleet ships turn out to be impervious to sensors, rendering them useless on many occasions. Species 8472 cannot be detected by the cutting edge sensors aboard the USS Voyager, but can still be seen by the plain old human eye. I hope that there are entire departments back at Starfleet Headquarters who do nothing but research upgrades to sensor technology, because those improvements are sorely needed.
Even scanning the interior of one’s own starship can lead to wildly varying results. Way back in TOS, the only way to find Albert Finney in the episode Court Martial was to get pretty much everyone else off the ship and then listen for his heartbeat. It made for a tense scene, but was there really nothing better available? Then again, Court Martial is the one and only episode where Captain Kirk has a special “jettison pod” button on the arm of the captain’s chair, so maybe the whole thing took place in an alternate timeline.
By the 24th century, things have moved on a bit, and crewmembers can usually be located simply by tracking down their comm badge. But for all that the sensors can also report on life signs, frequently all it takes is for someone to go ‘off grid’ is for them to take off their comm badge. While I’m willing to accept that one human life sign looks much like another, and finding one person out of several hundred could still take time, surely the system shouldn’t be so easy to defeat? You could track the progress of a human life sign from the point where they took off their comm badge. You could even use a shipboard CCTV to check on their whereabouts. Sure, CCTV in crew quarters would be an invasion of privacy, but it makes sense to have it installed in corridors and public areas – especially given how often unauthorised aliens sneak around.
Even the most ardent Star Trek fan would probably go mad trying to find in-universe reasons for why the sensors behave as they do, or why the crew thinks to use them in a particular way in one episode, and then fail to do so in the next. Nonetheless, when it comes to nitpicking minor continuity issues in our favourite sci-fi series, starship sensors promise to provide a rich vein of discussion for years to come.