At one point in my research of this film I was confronted with the possibility that it might not be a time travel story at all, but a story about someone who thinks he can time travel.  That in itself becomes one of the tensions in the film:  has Kenneth Calloway really secretly built a time machine, or is he lying or delusional?  If he has not, what is he really doing?  The answers to those questions wind up being the climax of the film, and so would be the ultimate spoilers, so they will be reserved for later in this series.  Besides, whether or not there is actual time travel, there are issues raised that are about time travel, how it would work and what those affected by it would experience, and we may be able to answer at least some of those points without giving away the answer.  As we discovered with Terminator Salvation, it is possible to address time travel issues without using any time travel in the movie.

Besides, there is a real sense in which this movie is not about time travel at all.  It is about relationships, and the idea that people need people, and must find someone with whom to connect.

It begins with Darius, a girl working an unpaid internship at Seattle Magazine, who has a very pessimistic view of life.  At a staff meeting, editor Bridget asks for story ideas, and cocky crass writer Jeff suggests following up on an ad someone placed in the magazine looking for a companion for time traveling.  Everyone assumes it is either a joke or a nut, but Jeff thinks it might be worth pursuing to get a humorous story from it, and gets Bridget to give him two interns and a budget to stay in Ocean View to investigate this.  He takes Darius, and another named Arnau, a biological sciences undergrad of near eastern extraction.  Darius does most of the work of identifying Kenneth as the person who placed the ad, and when Jeff manages to offend Kenneth trying to pretend he is interested in time travel, Darius makes contact and becomes involved in working with Kenneth to prepare for a trip to the past.

They both have personal mission goals, Darius to prevent the death of her mother, Kenneth to prevent the death of a girl he considers his high school girl friend.  There are complications in both of these stories, to be considered as our analysis progresses.

Meanwhile, some government agency has agents following Kenneth.  (They never identify themselves, but could be FBI or NSA.)  Their concerns arise from the facts that he asked a lot of government scientists a lot of questions about the Berkeley particle accelerator and was arrested for breaking into a nuclear physics laboratory in Colorado, and more recently by a robbery at a medical research facility nearby.  So it seems that Kenneth might be paranoid, but they really are out to get him.

All of this builds toward a climax in an enjoyable romp of a story in which no one knows quite what to think most of the time, but hopefully we will be able to untangle bits of it--and probably rather quickly.  We will try to delay the spoilers as long as possible, but as the title suggests, Safety Not Guaranteed.

The time travel story in Safety Not Guaranteed opens with an advertisement placed via the Internet in Seattle Magazine, looking for a time traveling companion.  The ad, read aloud in the film (and featured on the cover of the DVD), includes the statement,

I have only done this once before.

It is a puzzle in itself, because it is evident that he gets Darius to help him steal lasers from medical research facility GML Laser Technologies because he needs them for the time machine.  That suggests that the time machine is unfinished, and he could not have used it.  Perhaps, though, he needs the lasers to improve a machine which succeeded in a first test.  One can use lasers to enable cold fusion power, so it might be that his first trip used a single-use power source, but the lasers will enable him to make multiple trips.  Alternatively, he may be obtaining backup equipment in case something breaks while he is in the past.

That raises the question of where, or perhaps rather when, he went.  Assuming he made such a trip at all, it would have been a test trip, and therefore a short one.  On the other hand, because the machine travels in time but not space, and because it must be large enough to carry two passengers comfortably, he would need to move it away from where it was before it was there, so he would have to go back to before the machine was placed in its starting position and allow enough time to move it somewhere else.  On the other hand, the easier test trip is to the future.  It does not answer all the critical questions, as time travel to the future is much simpler than time travel to the past (we all do it every day, albeit at what we consider a rather slow rate).  It has, however, several advantages.  If it works, the machine will have vanished from the departure time and so not be there at the arrival time to be in its own way.  It might be necessary to make such a trip simply to calibrate the machine--to know how far through time you will travel for what inputs (just ask Blackadder).  Further, given Kenneth's paranoia, a leap to the future is a relatively simple way to evade surveillance or pursuit, as for whatever period you skip you simply do not exist anywhere.  In any case, most of us would want to check before we traveled any distance into the past to be certain we could return to the future.  There are plenty of stories of travelers trying to return to their own time, such as Blackadder Back and Forth, Timeline, Frequently Asked Questions About Time Travel, and of course the classic Back to the Future.  It would be quite reasonable for Kenneth to check whether his machine can travel forward before he determines whether it can go back.  Further, if he takes a short trip--an hour, a day, not more than a week--he need not make a return trip, and then he would quite literally have done it only once before.  Were he to make a trip to the past and not return to his own time, there would be a significant probability that his younger self, not yet having made the trip, would encounter if not his older self at least the rather large and difficult to hide duplicate time machine itself.

Ultimately, though, we do not know what he did, only that he claims to have tested the time machine and satisfied himself that it actually does what he hopes.  For all we know, he could have blown out all the circuits in the house and rendered himself unconscious, only to awaken sometime later and decide when he can learn what time it is that he must have traveled through time.

That's certainly more than we know about the first trip, other than that if it happened it was before the movie began and there is no way to know what happened during or because of it.

Kenneth Calloway eventually reveals his intended mission to Darius, who shares it with Jeff, who sends it back by e-mail to Bridget.  He plans to prevent the death of Belinda St. Sing, whom he identifies as his high school girlfriend, who he claims was killed by a drunk driver crashing a car into her living room.

To clarify who these people are, Darius is the female intern who actually connects with Kenneth, the supposed time traveler.  Her name is only mentioned once in the first half hour of the movie, and it is not clear when it is mentioned that it refers to her.  (Darius being a masculine Persian name and the other intern being of middle eastern or near eastern extraction, it is unclear whether this is one of Jeff's arrogant jokes.  That intern is named Arnau.)  Jeff is the writer who is officially doing the story, despite the fact that he spends most of the time trying to reconnect with an old flame from his own high school days.  Bridget is the editor back in Seattle who is waiting for the story.  She is the first to mention Belinda's name, but we infer that Kenneth mentioned it to Darius in a part of the conversation not shown.

When Bridget calls Jeff to check on the story, she tells him that Belinda is not dead, but alive, married, and living an hour away.  Darius makes the trip with the others to interview her, and in their conversation an accident similar to the one described by Kenneth is described.  It is different in these significant details:

1. Nobody died in Belinda's version; nobody was even seriously hurt.  In Kenneth's story, Belinda died.
2. The accident occurs at the home of Belinda's new boyfriend Rob, not at Belinda's house, and the house was damaged but not so seriously.
3. The driver in Belinda's accident is identified as young Kenneth, but no mention is made of anyone being drunk.  It may be that Kenneth omitted identifying himself in the original telling, or that Belinda did not mention he was drunk, but these points are not made.
4. Belinda never dated Kenneth; she was only nice to him because he was a nice guy, but she always thought him a bit odd, the kind of guy who wouldn't fit in her life.

What is interesting to us, though, is that when Darius confronts Kenneth with the fact that Belinda is alive, after he gets past denying it, he concludes that the trip he has not yet made must be successful.  That raises flags for us.

It tells us first that this cannot be a fixed time theory movie; if Kenneth is right, the past can be and in fact has been changed.

The odd point is that Belinda would be alive but Kenneth remember her having died.  Obviously Belinda did not just return to life; she has been alive since the accident.  She is alive because, at least in this history, she never died.  So why would Kenneth believe that she did die?  It is not even as if this is the Kenneth who went back and altered her history, such that he would remember the unaltered version--he has not yet attempted to save her.  Thus if she never died in this history, that would be what he remembered.  This thus cannot be a multiple dimension theory movie, because no matter how you read it, this has to be the Kenneth who lived in this dimension.  However, if we solve it by replacement theory, we have much the same problem:  this Kenneth has always lived in that history in which Belinda never died, and cannot remember the history in which she died.  In fact, he cannot be planning to save her, because he cannot know that she needs to be saved, and so we are headed for an infinity loop because if she is alive he will not make the trip to save her.

Thus the notion that Belinda is alive because Kenneth is going to change the past to save her is ultimately unworkable.  If she did not die in this history, he in this history cannot know she would have.

Let us suppose that indeed Belinda was dead and is alive.  That then creates another problem:  what of Darius' mother?

We might argue that since Kenneth has not yet traveled to the past to save Belinda, we cannot know whether Darius goes with him.  On that reasoning, though, we cannot know whether Kenneth himself makes the trip or saves Belinda, but the argument is that he does because she is alive.  If Darius' mother is not also still alive, then either she did not go with him or they did not save her.  However, from the moment Kenneth completes his first mission there is no version of events (following the causal chain) in which Darius does not go with Kenneth.

Perhaps, then, Kenneth already succeeded in saving Belinda, but did not know it.  He would have to have done so by whatever he did on that first trip, which seems improbable if anything we concluded about that trip is true, and the more so if saving Belinda is still his mission objective this time.  He might not remember that what he did changed the past such that Belinda is alive, but at least he should have recognized that his trip to that time must have altered events in a way that might have caused that change.  That he does not imagine that possibility--it is clearly in his mind that he has not yet done anything that could save her, but must do so yet in his own future--tells us that this is not what happened.

Perhaps they did, or will, save Darius' mother, but just as Kenneth is somehow shielded from knowing that Belinda is alive, so too Darius is shielded from knowing that her mother is.  How does that work, then?  Darius evidentally is not shielded against knowing that Belinda is alive, even though she must have been involved in saving her.  Perhaps it is simply that they do not know if they have no contact, and Kenneth (having always been involved in the accident) never again saw Belinda.  Yet it seems that Darius' father is equally unaware that her mother is still alive, and just as obviously had her mother lived Darius would have seen her probably every day for years thereafter.  But is it that her mother never died, but after talking to that ungrateful fourteen-year-old daughter decided she had better things to do with her life and simply never came home again, vanishing without a trace?  It is very difficult to imagine how her mother could still be alive and Darius not know this.

Perhaps, we are given to think, Kenneth is delusional.  There is no time travel, and the death of Belinda is entirely in his head, invented as a way of protecting himself from the fact that she was never his girlfriend.  They don't save Darius' mother because they did not save Belinda either.  That is the conclusion we reach if we believe that Kenneth has not created a time machine.  What, though, if he has?

We are left with the possibility that having determined to save both Belinda and Darius' mother, our intrepid duo succeeded in the first but not the second.  It would be a disappointment, and it is difficult to determine how they might be able to change history so dramatically in the first instance and not adequately in the second.  That makes this outcome also unlikely, but not impossible.

It also avoids the problem of an infinity loop, because if Darius is unable to change the past intentionally, she does not undo her own wish to do so, thus creating an N-jump.  However it happened, that is the best outcome.

We have delayed the spoilers as long as we might.  In the end, Kenneth and Darius board the time machine, it is surrounded by a bubble, and in a flash it vanishes before the eyes of Jeff, Arnau, and two government agents.  We do not know where our intrepid duo goes or what they do, whether indeed they are the reason Belinda is alive, whether they save Darius' mother.

Yet in the denoument behind the voice-overs of closing thoughts, we see Kenneth and Darius racing through the woods.  Maybe it is a flashback to their training.  Maybe it is a look at where they are going.  If it is the latter, it suggests that they have great adventures bouncing around through time.

That means trouble.

Certainly it is possible to visit the past and change nothing of significance.  However, thanks to the butterfly effect--the concept that small changes can have large consequences--the more times and places they visit, the more likely it is that they will change something that matters.  This is the more significant, given that Kenneth lives in what was his parents' home not far from the launch site, and the machine appears to remain stationary relative to the planet.  There is a good chance he will encounter if not himself his parents or ancestors.  We cannot guess what impact that might have.  He might severely alter his own life, even undo himself.

Or perhaps not.  A disaster might occur, but they might avoid it.

So we have some issues with Safety Not Guaranteed, but overall it is one of the better time travel movies.