The Trace

The Trace is a curious thing, one that could be placed in a few different sections of this reference work.

How does this operate? I think it has to be a detection ward of some sort. I have read number of different ideas about it.

Things we know:

• "small explosions from Fred and George’s bedroom were considered perfectly normal."¹ They are certainly doing under-aged magic of some sort (probably potions based).
• "they can detect magic, but not the perpetrator … They rely on witch and wizard parents to enforce their offspring’s obedience while within their walls.”²
• Dobby's magic can trigger it.³
• It is suggested that the Order is sneaking Harry out under the eyes of the Ministry,⁴ and yet Tonks' magic does not set it off in book five.⁵
• It automatically breaks at age seventeen.⁶ It is unknown if it could be put back on, if it is merely illegal to do so, or if it is impossible to do so.

Things we speculate:

• One author suggested that it gets added to wands that ride the Hogwarts Express.⁷ The problem with this is that I believe it would effect the wands of 7th year students, most if not all of whom are already 17.
• One author suggested it gets added (to either wands or students) as they ride the boats on their way to Hogwarts for the first time.⁸
• One author suggested there is a network of rune-engraved ward-stones across the country.⁹
• One author suggests that monitoring devices are placed near the address of witches and wizards known to be under-aged.¹⁰ The Trace then only works near such devices.
• A number of authors suggest that there is "equipment" at the Ministry that is used to detect magic. Some think that equipment can distinguish between under-aged and over aged magic.¹¹ This would effectively be an example of 17 as a magical number that effects the way magic operates at a fundamental level. Some think that the equipment is "tuned" to detect certain magic, and could be returned to detect different magic.¹² I am not sure that really differs.
• One interesting idea suggested that the trace, regardless of which of the above, only worked for wands in which the person requesting the report had an owning interest in, and thus the Ministry subsidised wand sales to minors.¹³ By paying for part of a child's wand, the Ministry has partial ownership and could thus get magical reports on the wand's use.
• Does the Trace work on the person's physical age, calendar age, or mental age?
  • If placed on a person with severe mental retardation, would it ever break?
  • If placed on a person (such as Hermione) who used a time turner, would it break early?

In all of my stories, I need to figure out which approach I am going to take, either one of the above, or some other approach. I dislike contradicting the text when it comes to world mechanics more than I have to. However, I do have to some - wizarding households function on magic, so the Decree for the Reasonable Restriction of Underage Sorcery and the Trace either allows for supervised household charm or does not function at all in wizarding households, probably the latter. The whole "do not use magic outside of school" thing is more for muggle born witches and wizards rather than any real restriction. See Culture for more on this.