"Stud finder" and "stud detector" are the same thing - two names for a tool that locates the wooden framing studs hidden behind your wall. There is no real difference in the terms. What actually matters is the detection method, and there are three, with very different accuracy. Here is how they compare.
A magnetic finder does not detect the wood stud at all. It detects the metal screws or nails that hold the drywall to the stud. The simplest ones are just a strong magnet that tugs toward a fastener; better ones use a moving rare-earth magnet for a clearer signal. Pros: cheap, tiny, no batteries, never breaks. Cons: you only find the fasteners, which are spaced out, so it takes patience to map the full stud.
An electronic finder has a capacitive density sensor that reads changes in density through the drywall. The wall plus a stud behind it is denser than the wall alone, and the sensor flags that change - so it detects the wood stud itself, not just the metal. This is the most accurate method for locating studs, especially their edges, and it is why electronic finders are the standard for load-bearing work. Better models read several sensors at once and show the full width of the stud.
A stud-finder app uses your phone's magnetometer - the compass sensor. Like a magnetic finder, it detects the metal fasteners, not the wood, because phones do not carry a density sensor. That makes phone apps accurate for metal and great for a free quick check, but less precise at pinpointing a wood stud than an electronic finder. On Android a good app works well; on iPhone, iOS blocks the sensor, so there is no reliable free app option.
For finding the wood stud itself: the electronic density finder, clearly. For confirming a fastener location cheaply: a magnetic finder or a phone app. The practical setup for most people is a free app for quick checks plus one good electronic finder for anything you are hanging weight on.
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