Should I Test Whether Someone Unfamiliar With My Car Can Detect the Fragrance Before Deciding My Freshener Has Stopped Working?

Yes, and I would go further: you should not make that decision any other way, because your own reading of your own cabin is the least reliable one available and it is wrong in a predictable direction. The reason is simple enough to state in a sentence and is explained properly on its own page in this family: a nose stops reporting a smell that never changes, and you are nearer the source and in the cabin longer than anybody else, so you are the first person it stops reporting to. Somebody arriving from outside has had their nose set by the street, so your cabin registers to them as a difference, which is the only thing a nose reports well. That makes them an instrument and you a bystander, and the rest of this page is about using the instrument correctly. Because here is the thing readers get wrong, and it ruins the result: they ask the wrong question. "Can you smell the fragrance in here?" is close to useless, for two reasons. It tells the person what you are interested in, so a polite passenger will search for it, find a trace, and confirm it - and a trace found on request is not the same finding as a cabin that smelled of something on entry. And it also tells them what answer would please you, which for most people is enough to shape the reply without them noticing. So you ask an open question instead: what do you notice about the car? If the cabin smells of fragrance, that is what people say, unprompted, in my experience almost every time. If they mention the seats or the traffic or nothing at all, that is a genuine negative and it is worth something. The timing matters almost as much as the wording. Ask within the first ten seconds of them getting in, because their own nose begins settling immediately on entering a scented space. A question asked five minutes into a journey has been answered by a nose that is already part-way adapted, which converts your reliable instrument into a slightly less unreliable version of you. And the choice of person is the part readers most often get wrong in good faith. The colleague who commutes with you every day is not a fresh nose. They have been sitting in your cabin as long as you have, minus the parked hours, and they will report what you report. Their silence about the fragrance is not evidence that it has gone. What you need is somebody who has not been in the car for a day or two: a visitor, a relative collected from a station, a colleague who takes a lift once a month, a friend you give a ride to after not seeing them for a while. Children are excellent for this and notably willing to say the cabin smells strongly of something, which is exactly the bluntness the test needs. Then put the reply beside one other reading, and that reading is also free: look at the liquid level. Not smell it, look at it. Those two readings together produce four combinations rather than two, and the four have different answers, which is why I set them out as a grid further down rather than as a yes-or-no. The short version is that only one of the four combinations is an instruction to buy anything, and it is not the one most readers expect. Finally, the case where there is nobody to ask, which is a sizeable minority of the people who write to me about this. You can approximate the instrument with a reset. Stay out of the car for about forty-eight hours, do not think about the question beforehand, then open the door and pay attention to the first ten seconds and nothing after that. It is weaker than a passenger because you know what you are hoping for, and it is still far better than a decision made on the memory of a smell. The entire protocol costs nothing and is the only reliable thing in this category, which is why this page has no product at the end of it.